29
An Experimental Study of Competitive Market Behavior Vernon L. Smith The Journal of Political Economy, Vol. 70, No. 2. (Apr., 1962), pp. 111-137. Stable URL: http://links.jstor.org/sici?sici=0022-3808%28196204%2970%3A2%3C111%3AAESOCM%3E2.0.CO%3B2-J The Journal of Political Economy is currently published by The University of Chicago Press. Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/about/terms.html. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/journals/ucpress.html. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. The JSTOR Archive is a trusted digital repository providing for long-term preservation and access to leading academic journals and scholarly literature from around the world. The Archive is supported by libraries, scholarly societies, publishers, and foundations. It is an initiative of JSTOR, a not-for-profit organization with a mission to help the scholarly community take advantage of advances in technology. For more information regarding JSTOR, please contact [email protected]. http://www.jstor.org Wed Sep 26 14:37:37 2007

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Page 1: An Experimental Study of Competitive Market Behavior Vernon L. …econ.ucsb.edu/~oprea/176/Competitive.pdf · 2007-09-26 · THE JOURNAL POLITICAL ECONOMY Volume LXX APRIL 1962 Number

An Experimental Study of Competitive Market Behavior

Vernon L Smith

The Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137

Stable URL

httplinksjstororgsicisici=0022-38082819620429703A23C1113AAESOCM3E20CO3B2-J

The Journal of Political Economy is currently published by The University of Chicago Press

Your use of the JSTOR archive indicates your acceptance of JSTORs Terms and Conditions of Use available athttpwwwjstororgabouttermshtml JSTORs Terms and Conditions of Use provides in part that unless you have obtainedprior permission you may not download an entire issue of a journal or multiple copies of articles and you may use content inthe JSTOR archive only for your personal non-commercial use

Please contact the publisher regarding any further use of this work Publisher contact information may be obtained athttpwwwjstororgjournalsucpresshtml

Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printedpage of such transmission

The JSTOR Archive is a trusted digital repository providing for long-term preservation and access to leading academicjournals and scholarly literature from around the world The Archive is supported by libraries scholarly societies publishersand foundations It is an initiative of JSTOR a not-for-profit organization with a mission to help the scholarly community takeadvantage of advances in technology For more information regarding JSTOR please contact supportjstororg

httpwwwjstororgWed Sep 26 143737 2007

T H E J O U R N A L

POLITICAL ECONOMY Volume L X X APRIL 1962 Number z

ZN EXPERIMENTAL STUDY OF COMPETITIVE MARKET BEHAVIOR1

VERNON L SMITH

Puldue University

I INTRODUCTION

RECENT years have witnessed a grow-ing interest in experimental games such as management de-

cision-making games and games designed to oligopolistic market phenom- ens hi^ article reports on a of experimental games desigrled to stuciy some of the hypotheses of neoclassical competitive market theory since the organized stock bond and commodity exchanges would seem to have the best chance of fulfilling the conditions of an operational theory of supply and de-mand most of these experiments have

The experiments on nhich this leport is based have been performed over a six-year period begin- ning in 1955 They are part of a continuing study in which the next phase is to include experimentation with monetary payoffs and more complicated ex-perimental designs to mhich passing references are made here and there in the present repo~t I wish to thank Mrs lIari lgtn Schweizer for assistance in typing and in the preparation of charts in this paper li K Davidson for perfor~ning one of the experi- ments for me and G Horwich J Hughes H Johnson and J bVolfe for reading an earlier version of the paper and enriching me with their comments and encouragement This work as supported by the Institute for Quanl~tatlve Keseatch at Purdue the luldue Research Founilation and in part by National Science Foundation Grant No 16114 a t Stanford Univelsity

been designed to simulate on a motlest scale the multilateral auction-trading process characteristic of these organized markets I would emphasize however that they are intended as simulations of certain key features of the organized markets and of competitive marketsgen- erally rather than as direct exhaustive simulations of any particular organized exchange The experimental conditions of and demand in force these markets are the

and demand curves gellerated by the limit price orders in the hands of stock and commodity market brokers a t the opening of a trading day in any Onestock or commodity tllough I would consider then1 to be good general models of received short-run supply and demand theory A similar experimental supply and demand model was first used by E H ChaInberlin iIl an illteresting set Of that pre-date contern-porary interest in experimelltal games

rn Experimental Impeifect Market Jo~~rilel of Political Economy LVI (April 1948) 95-108 For an experimental study of bilateral lnonopoly see S Siege1 and L Fouraker Bargai~iitgarzd GIOZCP Decision dfaking (New Yolk blcGran-Hill Book Co 1960)

111

Chamberlins paper was highly sugges- tive in demonstrating the potentialities of experimental techniques in the study of applied market theory

Parts I1 and I11 of this paper are devoted to a descriptive discussion of the experiments and some of their detailed results Parts IV and V present an em- pirical analysis of various equilibrating hypotheses and a rationalization of the hypothesis found to be most successful in these experiments

Part VI provides a brief summary which the reader may wish to consult before reading the main body of the paper

11 EXPERIMENTAL PROCEDURE

The experiments discussed in Parts I11 and IV have followed the same gen- eral design pattern The group of subjects is divided a t random into two subgroups a group of buyers and a group of sellers Each buyer receives a card containing a number known only to that buyer which represents the maximum price he is willing to pay for one unit of the fictitious commodity It is explained that the buyers are not to buy a unit of the commodity a t a price exceeding that appearing on their buyers card they would be quite happy to purchase a unit a t any price below this number-the lower the better but they would be entirely willing to pay just this price for the commodity rather than have their wants go unsatisfied I t is further ex-plained that each buyer should think of himself as making a pure pro6 t equal to the difference between his actual con- tract price and the maximum reserva- tion price on his card These reservation prices generate a demand curve such as DL) in the diagram on the left in Chart 1 At each price the correspond- ing quantity represents the maximum amount that could be purchased a t that

price Thus in Chart 1 the highest price buyer is willing to pay as much as $325 for one unit At a price above $325 the demand quantity is zero and a t $325 it cannot exceed one unit The next highest price buyer is willing to pay $300 Thus a t $300 the demand quantity cannot exceed two units The phrase cannot exceed rather than is will be seen to be of no small impor- tance How much is actually taken a t any price depends upon such important things as how the market is organized and various mechanical and bargaining considerations associated with the offer- acceptance process The demand curve therefore defines the set (all points on or to the left of DD) of possible demand quantities a t each strictly hypothetical ruling price

Each seller receives a card containing a number known only to that seller which represents the minimum price a t which he is willing to relinquish one unit of the commodity I t is explained that the sellers should be willing to sell a t their minimum supply price rather than fail to make a sale but they make a pure profit determined by the excess of their contract price over their mini- mum reservation price Under no con- dition should they sell below this mini- mum These minimum seller prices gen- erate a supply curve such as SS in Chart 1 At each hypothetical price the cor-responding quantity represents the maxi- mum amount that could be sold a t that price The supply curve therefore de- fines the set of possible supply quantities a t each hypothetical ruling price

In experiments 1-8 each buyer and seller is allowed to make a contract for the exchange of only a single unit of the commodity during any one trading or market period This rule was for the sake of simplicity and was relaxed in

EXPERIMENTAL STUDY OF COMPETITIVE MARKET BEHAVIOR 113

subsequent experiments Each experiment was conducted over

a sequence of trading periods five to ten minutes long depending upon the number of participants in the test group Since the experiments were conducted within a class period the number of trading periods was not uniform among

has been closed and the buyer and seller making the deal drop out of the market in the sense of no longer being permitted to make bids offers or contracts for the remainder of that market p e r i ~ d ~ As soon as a bid or offer is accepted the contract price is recorded together with the minimum supply price of the seller

CHART 1

TEST 1

the various experiments In the typical experiment the market opens for trad- ing period 1 This means that any buyer (or seller) is free a t any time to raise his hand and make a verbal offer to buy (or sell) a t any price which does not violate his maximum (or minimum) reservation price Thus in Chart 1 the buyer holding the $250 card might raise his hand and shout Buy a t $100 The seller with the $150 card might then shout Sell a t $360 Any seller (or buyer) is free to accept a bid (or offer) in which case a binding contract

and the maximum demand mice of the buyer involved in the transaition These observations represent the recorded data of the e~periment~ Within the time limit

All purchases are for final consumption There are no speculative purchases for resale in the same or later periods There is nothing however to pre- vent one from designing an experiment in which purchases for resale are permitted if the objective is to study the role of speculation in the equilibrating process One could for example permit the carry- over of s t d s from one period to the next

Owing to limitations of manpower and equip- ment in experiments 1-8 bids and offers which did not lead to transactions could not be recorded In subsequent experiments a tape recorder was used for this purpose

114 -ERNOX I SlITTII

of a trading period this procedure is continued until bids and ofters are no longer leading to contracts One or two calls are made for final bids or offers and the market is officially closed This ends period 1 The market is then im- mediately reopened for the second day of trading All buyers including those who did and those who did not make coiltracts in the preceding trading period i ~ o x ~ ~(as explained previously to the sub- jects) have a renewed urge to buy one unit of the commodity For each buyer the same maximum buying price holds in the second period as prevailed in the first period In this way the experimental demand curve represents a demand per unit time or per trading period Similarly each seller we may imagine has over- night acquired a fresh unit of the com- modity which he desires to sell in period 2 under the same minimum price con-ditions as prevailed in period 1 The experimental supply curve thereby repre- sents a willingness to supply per unit time Trading period 2 is allowed to run its course arlcl then period 3 and so on By this means we construct a prototype market in which there is a flow of a commodity onto and off the market The stage is thereby set to study price behavior under given conditions of nor- mal supply and demand5 Some buyers and sellers it should be noted may be unable to make contracts in any trading period or perhaps only in certain peri- ods Tnsofar as these traders are sub-marginal buyers or sellers this is to be eupected Indeed the ability of these experimental markets to ration out sub- marginal buyers and sellers will be one measure of the effectiveness or competi- tive performance of the market

The above design considerations define a rejection set of offers (and bids) for each I~uyer (and seller) which in turn

defines a demand and a supply schedule for the marliet in question-These sched- ules do nothing beyond setting extreme limits to the observable price-quantity behavior in that marliet All we can say is that the area above the supply curve is a region in which sales are feasible while tvhe area below the demand curve is a region in which purchases are feasi- ble ~ ~ m ~ e t i t i v e price theory asserts that there will be a tendency for price-quan- tity equilibrium to occur a t the extreme quantity point of the intersection of these G o areas For example in Chart 1 the shaded triangular area APB represents the intersection of these feasible sales and purchase sets with P the extreme point of this set We have no guarantee that the equilibrium defined by the inter- section of these sets will prevail even approximately in the experimental mar- ket (or any real counterpart of it) The mere fact that by any definition supply and demand schedules exist in the back- ground of a market does not guarantee that any meaningful relationship exists

The design of my experiments differs from that of Chamberlin (op cit) in several ways I n Chamber- lms experinlent the buyers and sellers simply cir- culate and engage in bilateral higgling and bargaining until they make a contract or the trading perioti ends As contracts are made the transaction price is recorded on the blackboard Consecluently there is very little if any multilateral bidding Each traders attention is directed to the one person with whom he is bargaining nhereas in my experiments each traders quotation is addressed to the entire trading group one quotation a t a time Also Cham- berlins experiment constitutes a pure exchange mar- ket operated for a single trading period There is therefore less opportunity for traders to gain experience and to modify their subsequent behavior in the light of such experience I t is only through some learning mechanism of this kind that I can imagine the possibility of equilibrium being ap-proached in any real market Finally in the present experiments I have varied the design from one experiment to another in a conscious attempt to study the effect of different conditions of supply and demand changes in supply or demand and changes in the rules of market organization on market-price behavior

ESPERIRlTSTL STTI)Y OF COLIPETITIIlt RI 4RKET BEH ITOR 115

between those schedules and what is ob- served in the market they are presumed to represent =11 the supply and demand schedules can do is set broad limits on the behavior of the market6 Thus in the symmetrical supply and demand dia- gram of Chart 3 it is conceivable that every buyer ant1 seller could make a contract The $325 buyer could buy from the $325 seller the $300 buyer could buy from the $300 seller and so forth wiihout violating any restrictions on the behavior of buyers and sellers Tntleed if we separately paired buyers and sellers in this special way each pair could be expectetl to make a bilateral contract a t the sellers miilimum price which ~voulti be equal to the buyers maximum price

I t should be noted that these e s ~ e r i - ments conform in several important ways to what we know must be true of many kinds of real markets In a real competi- tive market such as a commodity or stock exchange each marketer is likely to be ignorant of the reservation prices a t which other buyers and sellers are willing to trade Furthermore the only m y that a real marketer can obtain 1tiowletlge of market conditions is to

V n fact these schetlues are motiiiled as trading takes place Vhenevci- a ljuyer and a seller make a contract and drol) out of the market the demancl and supl)ly schetlules are shifted to the left in a nianner tlepentli~lg upon tlie buyers atid sellers position on the schetlules Iience the supply and tiemand ru~ictions co~itinually alter as the trading process occul-s I t is ~IiLhc~~it to imagine a real market ~xoccss which does not exhibit this characteristic Ihis means that the intra-trading-~~eriotl schedules are not iridepentlent of the transac~ions taking place FIo-ever the iiziiial schedules prevailirig a t the openilig of each trading period are independent of the transactions and it is these schedules that I identify with the theoretical conditions of supply and tlcmand which the theorist delines independ- ently of actual niarket prices and quantities One ol the importallt ol~jrctives in these experiments is to determine whether or not these irlitial schetlules have any power to ~)retlict the observetl behavior ol the market

observe the offers and bids that are ten- dered and whether or not they are ac- cepted These are the public data of the market A marketer can only know his own attitude and from observation learn something about the objective be- havior of others This is a major feature of these experimental markets We de- liberately avoid placing a t the disposal of our subjects any information which would not be practically attainable in a real market Each experimental market is forced to provide all of its own his- tory These markets are also a replica of real markets in that they are com-posed of a practical number of market- ers say twenty thirty or forty We do not require an indefinitely large number of marketers ~v l~ ich is usually supposed necessary for the existence of pure competition

One important condition operating in our experimental markets is not likely to prevail in real markets The experi- mental conditions of supply and demand are held constant over several successive trading periods in order to give any equilibrating mechanisms an opportuni- ty to establish an equilibrium over time Real markets are likely to be continu- ally subjected to changing conditions of supply and demand hlarshall was well aware of such problems and defined equi- librium as a condition toward which the market would move if the forces of sup- ply and demand were to remain station- ary for a sufficiently long time I t is this concept of equilibrium that this par- ticular series of experiments is designed in part to test There is nothing to prevent one from passing out new buyer andor seller cards representing changed demand andor supply conditions a t the end of each trading period if the objective is to study the effect of such constantly changing conditions on market behavior

In three of the nine experiments once- for-all changes in demand andor supply were made for purposes of studying the transient dynamics of a markets re-sponse to such stimuli

111 DESCRIPTION A h D DISCUSSION

OF E X P E R I M E N T A L RESULTS

The supply and demand schedule for each experiment is shown in the diagram on the left of Charts 1-10 The price and quantity a t which these schedules intersect will be referred to as the pre- dicted or theoretical equilibrium price and quantity for the corresponding ex- perimental market though such an equilibrium will not necessarily be attained or approached in the market The performance of each experimental market is summarized in the diagram on the right of Charts 1-10 and in Table 1 Each chart shows the sequence of contract or exchange prices in the order in which they occurred in each trading period Thus in Chart 1 the first transaction was effected a t $170 the second a t $180 and so on with a total of five transactions occurring in trading period 1 These charts show con- tract price as a function of transaction number rather than calendar time the latter of course being quite irrelevant to market dynamics

The most striking general characteris- tic of tests 1-3 5-7 9 and 10 is the remarkably strong tendency for exchange prices to approach the predicted equi- librium for each of these markets As the exchange process is repeated through successive trading periods with the same conditions of supply and demand pre- vailing initially in each period the varia- tion in exchange prices tends to decline and to cluster more closely around the equilibrium In Chart 1 for esample the variation in contract prices over the five

trading periods is from $170 to $225 The maximum possible variation is from $075 to $325 as seen in the supply and demand schedules As a means of measuring the convergence of exchange prices in each market a coefficient of convergence a has been coi~~puted for each trading period in each market The a for each trading period is the ratio of the standard deviation of exchange prices a to the predicted equilibriun~ price Po the ratio being expressed as a percentage That is a = 100 aolPo where a is the standard deviation of exchange prices around the equilibrium price rather than the mean exchange price Hence a provides a 111easure of exchange price variation relative to the predicted equilibrium exchange price is is seen in Table 1 and the charts for all tests except test 8 a tends to decline from one trading period to the next with tests 2 4A 5 6A 7 9A and 10 showing monotone convergence

Turning now to the individual experi- mental results it will be observed that the equilibrium price and quantity are approxin~ately the same for the supply and demand curves of tests 2 and 3 The significant difference in the design of these two tests is that the supply and demand schedules for test 2 are relatively flat while the corresponding schedules for test 3 are much more steep- ly inclined

Under the Walrasian hypothesis (the rate of increase in exchange price is an increasing function of the excess demand a t that price) one would expect the market in test 2 to converge more rapidly than that in test 3 As is evident from comparing the results in Charts 2 and 3 test 2 shows a more rapid and less er- ratic tendency toward equilibrium These results are of course cnnristent with many otller hypotheses including the

Irc- Coef- Ao of Sub Xo of SUE I clicted r~Luill ficient marginalAverage No of Sub- marginal s o of Sub-

Ex- Ex- of Con- H u q e ~ sActual marginal Sellers marginal clrdngc chaigc vergence n h oI ~ ~ ~ l ~ a n g c lloyers ho Sellers Qunn-

t i t y (30)

Quan-t i ty (XI

[a=

(100 un) (Po)I

Could AIaBc

Contractb

Price (r)

Who lade Coritracts

Could M a k e

Con t racts

Viio hladc Colltracts

---- -1-

1 6 5 5 6 3 5 6 5 5 6 7 5 6 6 5

15 16 4 15 15 4 15 16 4

16 17 5 16 5 16 5 16 3

10 None xone None Kone 10 None h-one xone None 10 None None Kone hTone 10 None Kone None None

8 None None None 8 None None None 8 None None None

10 10 10 10

12 12

12 None 12 Kone 12 hone 12 None

None None None None None None None hone Kone hone hTone None

xone None None None xone None

352 103 3 3 2

317 110 4 2 None None 336 3 2 4 1 None Kone 338 2 2 4 0 None None

CHART 2

0 2 4 6 8 10 12 14 16 18 20 2 2 1 4 8 12 17 4 8 12 15 4 O I 15 1 8 i 19

QUANTITY TRAN6ACTiC)N I 4 l i l G F i l I b Y P Rlgtl

excess-rent hypothesis to be discussed later7

The tests in Chart 4 are of special interest from the point of view of the Walrasian hypothesis In this case the supply curve is perfectly elastic-all sell-ers have cards containing the price $310 Each seller has the same lower bound on his reservation price acceptance set

equilibrium since there is a considerable excess supply a t prices just barely above the equilibrium price From the results we see that the market is not particularly slow in converging but i t converges to a fairly stable price about $020 above the predicted equilibrium Furthermore in test 4B which was an extension of 4A the interjection of a decrease in

CHART 4

TEST 4 A AND TEST 48 I6 C O I

- -- --- -580 -560 -5 4 0 - s

520 -

-5 00

Po 1310 Xo10

4 6 0 -

4 2 0 -u

2- 4 3 0 -+DECREASE

3 s o -

3 6 3 -

3 4 0

3 20

300

2 8 0

2 2 0 I

$ 6 0 0

5 80

560

5 4 0

5 2 0

5 0 0

4 80

460

4 4 0

4 20

IN DEMAYD+- O0

3 80

360

3 4 0

3 2 0

- 280

200 1 2 3 4 5 6 7 8 9 10 11 12 1 3 3 5 7 V I 3 5 7 V 1 3 5 7 9 1 3 5 7 9 1 3 5 7 8 1 3 5 7 1 3 5 6

Q ~ I A U T I T Y

In thi5 senie 11erc is no tlivergencc of attitude among the sellers though there might be marked variation in their bar- gaining propensities According to the Walrasian hypothesis this market should exhibit rapid convergence toward the

I T h e results are inconsistent n i t h the so-called hfarshallian hypothesis (the rate of increase in quan- tit) exchanged is an increasing function of the excess of demand price over supply price) but this hy- pothesis nould seem to be worth considering only in market processes in which some quantity-adjust- ing decision is made by the marketers The results of a pilot experiment in short-run and long-run equilibrium are displayed in the Appendix

TRANSACTION NUMBER ( B Y PERIOD1

demand from DD to DID was ineffective as a means of shocking the market down to its supply and demand equilibrium This decrease in demand was achieved by passing out new buyer cards corre- sponding to DD a t the close of period

in test 4A As the market approaches equilibrium from above since contracts a t prices below equilibrium are

The sellers in this market presented 3 solid front against price being lowered to ecluilibrium In the previous mar-

120 VERNON L SYIITFT

kets there was a divergence of seller attitude so that only a very few mar- ginal and near-marginal sellers might offer serious resistance to price being forced to equilibrium And this resistance tended to break down when any of the stronger intramarginal sellers accepted contracts below equilibrium

From these results it is clear that the static competitive market equilibri- um may depend not only on the inter- section of the supply and demanci sched- ules but also upon the shapes of the schedules Specifically I was led from test 4 to the tentative hypothesis that there may be an upward bias in the equilibrium price of a market which will be greater the more elastic is the supply schedule relative to demand8 For example let A be the area under the demand schedule and above the theoreti- cal equilibrium This is Alarshalls con-sumer surplus but to avoid any welfare connotations of this term I shall refer to the area as buyers rent Let B be the area above the supply schedule and below the theoretical equilibrium (Marshalls producer surplus) which I shall call sellers rent Now the tenta- tive hypothesis was that the actual mar- ket ecjuilibrium will be above the the- oretical equilibrium by an amount which depends upon how large A is relative to B Similarly there will be a downward bias if A is small relative to B

Test 4 is of course an extreme case since B = 0 In test 3 A is larger than B and the trading periods 3 and 4 ex-hibit a slight upward bias in the average actual exchange price (see Table 1) This provides some slight evidence in favor of the hypothesis

8 Note that the LValrasian hypothesis might lead one to expect a dol~nward bias since excess supply is very large at prices above equilihriuni if sup1)ly is very elastic relative to demand

As a consequence of these considera- tions test 7 was designed specifically to obtain additional information to sup- port or contradict the indicated hypothe- sis In this case as is seen in Chart 7 (see below) buyers rent is substan- tially smaller than sellers rent From the resulting course of contract prices over six trading periods in this experi- ment it is evident that the convergence to equilibrium is very slow From Table 1 the average exchange prices in the last three trading periods are respec- tively $332 $333 and $334 Average contract prices are still exhibiting a grad- ual approach to equilibrium Hence i t is entirely possible that the static equi- librium would eventually have been at- tained A still smaller buyers rent may be required to provide any clear down- ward bias in the static equilibrium One thing however seems quite unmistak- able from Chart 7 the relative magni- tude of buyers and sellers rent affects the speed with which the actual market equilibrium is approached One would expect sellers to present a somewhat weaker bargaining front especially a t first if their rent potential is large rela- tive to that of buyers Thus in Chart 7 i t is seen that several low reservation price sellers in trading periocls 1 and 2 made contracts a t low exchange prices which no doubt seemed quite profit- able to these sellers However in both these trading periods the later exchange prices were much higher revealing to the lour-price sellers that however prof- itable their initial sales had been still greater proLts were possible under stiffer bargaining

-4 stronger test of the hypotheses that buyer and seller rents affect the speed of adjustment and that they affect the final equil1rillln in the market would t)e ohtainal~lc l)j-introclucing actual mon-

etary payoffs in the experiment Thus one might offer to pay each seller the difference between his contract price and his reservation price and each buyer the difference between his reservation price and his contract price In addition one might pay each trader a small lump sum (say $005) just for making a contract in any period This sum would represent

GJeYTITi

iinormal pro~its that is a small return even if the good is sold a t its minimum supply price or purchased a t its maxi- mum demand price The present experi- ments have not seemeti to provide any motivation problems The subjects have shown high motivation to do their best even without monetary payo-tis But our experimental marginal buyers and sellers may be more reluctant to approach their reservation prices than their counter-parts in real markets The use oi nlone-tary payoifs as suggested should remox c

any such reluctance that is attributable to artificial elements in the present cx-peri i~lents ~

The experinlent summarized in Chart 5 was designed to study the effect on market behavior of changes in the condi- tions of demand and supply As it hap- pened this ex1)eriment was performed on a considerably more mature group

T R A N S A C T O N NJMBER ( 3 1 Pi11331

of subjects than any of the other experi- rnents Alost of the experiments were performed on sophornore ant1 junior en-gineering economics and business ma-jors while test 5 was performed on a

Since this was witten an experiment has been tried using monetary payofis and the same supply and demand design shown in Chart 4 The result as conjectured in the text TYas to remove the reluc- tance of sellers to sell at their reservation prices Ey the second trading period the market vas firmly in equilibrium In the thirtl period all trades were at $3ti) Al)parcntly$005 per pcriocl as considerecl satisfactory normal prolit

graduate class in econoinic theory 111

view of this dilference it is most interest- ing to find the phenomenally low values for a exhibited by test 5A The coefficient of convergence is smaller for the opening and later periods of this inarket than for any period of any of the other tests Furthermore trading periods 2-4 show as of less than 1 per cent indicating an inordinately strong and rapid tenden- cy toward equilibrium In this case no offers or bids were accepted until the bidding had converged to prices which were very near indeed to the ecluilibrium Contract prices ranged from $300 to S320 as compared with a possible range from $210 to $375

-It the close of test 5A new cards were distributed correspontling to an increase in demand from DD to DID as shown in Chart 51deg The subjects of course could guess from the fact that new buy- er cards were being distributed that a change in demand was in the wind But they knew nothing of the direction of change in demand except what might be guessed by the buyers from the al- teration of their individual reserv a t ion prices When trading began (period 1 test 5B) the immediate response was a very considerable upward sweep in exchange prices with several contracts being closed in the first trading period well above the new higher ecluilibrium price Indeed the eagerness to buy was so strong that two sellers who were submar- ginal both before and after the increase in demand (their reservation prices were

W o t e also that there was a small (one-unit) decrease in supply from SS to SS This was not planned It was due to the inal~ility of one sul~ject (the seller with the $210 reservation price) in test 5A to participate in test 5B Therefore except for the deletion of this one seller from the market the conditions of supply r e r e not altered that is the scllc~s ol test 5 B retni~~cclthe same rcscrvation 1)ricc cards as they liad ill test 51

$350 and $370) were able to m~bc con- tracts in this transient phase of the mar- ket Consecluently the trading group showing the strongest equilibrating ten- dencies exhibited very erratic behavior in the transient phase following the in- crease in demand Contract prices greatly overshot the new equilibrium and ration- ing by the market was less efficient in this transient phase In the second tratl- ing period of test 5B no submarginal sellers or buyers made contracts and tllc inarket exhibited a narrowed movcment toward the new equilibrium

Test 611 was designed to determine whether market equilibrium was affected by a marlred imbalance between the number of intramarginal sellers and the number of intramarginal buyers near the predicted equilibrium price The demand curve DD in Chart 6 falls continuously to the right in one-unit steps while the supply curve SS becomes perfectly in- elastic a t the price $400 well below the equilibrium price $1075 The tenta- tive hypothesis was that the large rent ($675) enjoyed by the marginal seller with still larger rents for the intramar- ginal sellers might prevent the theoreti- cal equilibrium from being established From the results it is seen that the earlier conjecture concerning the efiect of a divergence between buyer and seller rent on the approach to equilibrium is confirmed The approach to ecluilibrium is from below and the convergence is relatively slow However there is no indication that the lack of marginal sell- ers near the theoretical equilibrium has prevented the equilibrium from being attained The average contract price in trading period 4 is $1090 only $015 above the predicted equilibrium

4t the close of trading period 4 in test 611 thc old buyer cards correspond- ing to DD were rcplaced by new cards

correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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Page 2: An Experimental Study of Competitive Market Behavior Vernon L. …econ.ucsb.edu/~oprea/176/Competitive.pdf · 2007-09-26 · THE JOURNAL POLITICAL ECONOMY Volume LXX APRIL 1962 Number

T H E J O U R N A L

POLITICAL ECONOMY Volume L X X APRIL 1962 Number z

ZN EXPERIMENTAL STUDY OF COMPETITIVE MARKET BEHAVIOR1

VERNON L SMITH

Puldue University

I INTRODUCTION

RECENT years have witnessed a grow-ing interest in experimental games such as management de-

cision-making games and games designed to oligopolistic market phenom- ens hi^ article reports on a of experimental games desigrled to stuciy some of the hypotheses of neoclassical competitive market theory since the organized stock bond and commodity exchanges would seem to have the best chance of fulfilling the conditions of an operational theory of supply and de-mand most of these experiments have

The experiments on nhich this leport is based have been performed over a six-year period begin- ning in 1955 They are part of a continuing study in which the next phase is to include experimentation with monetary payoffs and more complicated ex-perimental designs to mhich passing references are made here and there in the present repo~t I wish to thank Mrs lIari lgtn Schweizer for assistance in typing and in the preparation of charts in this paper li K Davidson for perfor~ning one of the experi- ments for me and G Horwich J Hughes H Johnson and J bVolfe for reading an earlier version of the paper and enriching me with their comments and encouragement This work as supported by the Institute for Quanl~tatlve Keseatch at Purdue the luldue Research Founilation and in part by National Science Foundation Grant No 16114 a t Stanford Univelsity

been designed to simulate on a motlest scale the multilateral auction-trading process characteristic of these organized markets I would emphasize however that they are intended as simulations of certain key features of the organized markets and of competitive marketsgen- erally rather than as direct exhaustive simulations of any particular organized exchange The experimental conditions of and demand in force these markets are the

and demand curves gellerated by the limit price orders in the hands of stock and commodity market brokers a t the opening of a trading day in any Onestock or commodity tllough I would consider then1 to be good general models of received short-run supply and demand theory A similar experimental supply and demand model was first used by E H ChaInberlin iIl an illteresting set Of that pre-date contern-porary interest in experimelltal games

rn Experimental Impeifect Market Jo~~rilel of Political Economy LVI (April 1948) 95-108 For an experimental study of bilateral lnonopoly see S Siege1 and L Fouraker Bargai~iitgarzd GIOZCP Decision dfaking (New Yolk blcGran-Hill Book Co 1960)

111

Chamberlins paper was highly sugges- tive in demonstrating the potentialities of experimental techniques in the study of applied market theory

Parts I1 and I11 of this paper are devoted to a descriptive discussion of the experiments and some of their detailed results Parts IV and V present an em- pirical analysis of various equilibrating hypotheses and a rationalization of the hypothesis found to be most successful in these experiments

Part VI provides a brief summary which the reader may wish to consult before reading the main body of the paper

11 EXPERIMENTAL PROCEDURE

The experiments discussed in Parts I11 and IV have followed the same gen- eral design pattern The group of subjects is divided a t random into two subgroups a group of buyers and a group of sellers Each buyer receives a card containing a number known only to that buyer which represents the maximum price he is willing to pay for one unit of the fictitious commodity It is explained that the buyers are not to buy a unit of the commodity a t a price exceeding that appearing on their buyers card they would be quite happy to purchase a unit a t any price below this number-the lower the better but they would be entirely willing to pay just this price for the commodity rather than have their wants go unsatisfied I t is further ex-plained that each buyer should think of himself as making a pure pro6 t equal to the difference between his actual con- tract price and the maximum reserva- tion price on his card These reservation prices generate a demand curve such as DL) in the diagram on the left in Chart 1 At each price the correspond- ing quantity represents the maximum amount that could be purchased a t that

price Thus in Chart 1 the highest price buyer is willing to pay as much as $325 for one unit At a price above $325 the demand quantity is zero and a t $325 it cannot exceed one unit The next highest price buyer is willing to pay $300 Thus a t $300 the demand quantity cannot exceed two units The phrase cannot exceed rather than is will be seen to be of no small impor- tance How much is actually taken a t any price depends upon such important things as how the market is organized and various mechanical and bargaining considerations associated with the offer- acceptance process The demand curve therefore defines the set (all points on or to the left of DD) of possible demand quantities a t each strictly hypothetical ruling price

Each seller receives a card containing a number known only to that seller which represents the minimum price a t which he is willing to relinquish one unit of the commodity I t is explained that the sellers should be willing to sell a t their minimum supply price rather than fail to make a sale but they make a pure profit determined by the excess of their contract price over their mini- mum reservation price Under no con- dition should they sell below this mini- mum These minimum seller prices gen- erate a supply curve such as SS in Chart 1 At each hypothetical price the cor-responding quantity represents the maxi- mum amount that could be sold a t that price The supply curve therefore de- fines the set of possible supply quantities a t each hypothetical ruling price

In experiments 1-8 each buyer and seller is allowed to make a contract for the exchange of only a single unit of the commodity during any one trading or market period This rule was for the sake of simplicity and was relaxed in

EXPERIMENTAL STUDY OF COMPETITIVE MARKET BEHAVIOR 113

subsequent experiments Each experiment was conducted over

a sequence of trading periods five to ten minutes long depending upon the number of participants in the test group Since the experiments were conducted within a class period the number of trading periods was not uniform among

has been closed and the buyer and seller making the deal drop out of the market in the sense of no longer being permitted to make bids offers or contracts for the remainder of that market p e r i ~ d ~ As soon as a bid or offer is accepted the contract price is recorded together with the minimum supply price of the seller

CHART 1

TEST 1

the various experiments In the typical experiment the market opens for trad- ing period 1 This means that any buyer (or seller) is free a t any time to raise his hand and make a verbal offer to buy (or sell) a t any price which does not violate his maximum (or minimum) reservation price Thus in Chart 1 the buyer holding the $250 card might raise his hand and shout Buy a t $100 The seller with the $150 card might then shout Sell a t $360 Any seller (or buyer) is free to accept a bid (or offer) in which case a binding contract

and the maximum demand mice of the buyer involved in the transaition These observations represent the recorded data of the e~periment~ Within the time limit

All purchases are for final consumption There are no speculative purchases for resale in the same or later periods There is nothing however to pre- vent one from designing an experiment in which purchases for resale are permitted if the objective is to study the role of speculation in the equilibrating process One could for example permit the carry- over of s t d s from one period to the next

Owing to limitations of manpower and equip- ment in experiments 1-8 bids and offers which did not lead to transactions could not be recorded In subsequent experiments a tape recorder was used for this purpose

114 -ERNOX I SlITTII

of a trading period this procedure is continued until bids and ofters are no longer leading to contracts One or two calls are made for final bids or offers and the market is officially closed This ends period 1 The market is then im- mediately reopened for the second day of trading All buyers including those who did and those who did not make coiltracts in the preceding trading period i ~ o x ~ ~(as explained previously to the sub- jects) have a renewed urge to buy one unit of the commodity For each buyer the same maximum buying price holds in the second period as prevailed in the first period In this way the experimental demand curve represents a demand per unit time or per trading period Similarly each seller we may imagine has over- night acquired a fresh unit of the com- modity which he desires to sell in period 2 under the same minimum price con-ditions as prevailed in period 1 The experimental supply curve thereby repre- sents a willingness to supply per unit time Trading period 2 is allowed to run its course arlcl then period 3 and so on By this means we construct a prototype market in which there is a flow of a commodity onto and off the market The stage is thereby set to study price behavior under given conditions of nor- mal supply and demand5 Some buyers and sellers it should be noted may be unable to make contracts in any trading period or perhaps only in certain peri- ods Tnsofar as these traders are sub-marginal buyers or sellers this is to be eupected Indeed the ability of these experimental markets to ration out sub- marginal buyers and sellers will be one measure of the effectiveness or competi- tive performance of the market

The above design considerations define a rejection set of offers (and bids) for each I~uyer (and seller) which in turn

defines a demand and a supply schedule for the marliet in question-These sched- ules do nothing beyond setting extreme limits to the observable price-quantity behavior in that marliet All we can say is that the area above the supply curve is a region in which sales are feasible while tvhe area below the demand curve is a region in which purchases are feasi- ble ~ ~ m ~ e t i t i v e price theory asserts that there will be a tendency for price-quan- tity equilibrium to occur a t the extreme quantity point of the intersection of these G o areas For example in Chart 1 the shaded triangular area APB represents the intersection of these feasible sales and purchase sets with P the extreme point of this set We have no guarantee that the equilibrium defined by the inter- section of these sets will prevail even approximately in the experimental mar- ket (or any real counterpart of it) The mere fact that by any definition supply and demand schedules exist in the back- ground of a market does not guarantee that any meaningful relationship exists

The design of my experiments differs from that of Chamberlin (op cit) in several ways I n Chamber- lms experinlent the buyers and sellers simply cir- culate and engage in bilateral higgling and bargaining until they make a contract or the trading perioti ends As contracts are made the transaction price is recorded on the blackboard Consecluently there is very little if any multilateral bidding Each traders attention is directed to the one person with whom he is bargaining nhereas in my experiments each traders quotation is addressed to the entire trading group one quotation a t a time Also Cham- berlins experiment constitutes a pure exchange mar- ket operated for a single trading period There is therefore less opportunity for traders to gain experience and to modify their subsequent behavior in the light of such experience I t is only through some learning mechanism of this kind that I can imagine the possibility of equilibrium being ap-proached in any real market Finally in the present experiments I have varied the design from one experiment to another in a conscious attempt to study the effect of different conditions of supply and demand changes in supply or demand and changes in the rules of market organization on market-price behavior

ESPERIRlTSTL STTI)Y OF COLIPETITIIlt RI 4RKET BEH ITOR 115

between those schedules and what is ob- served in the market they are presumed to represent =11 the supply and demand schedules can do is set broad limits on the behavior of the market6 Thus in the symmetrical supply and demand dia- gram of Chart 3 it is conceivable that every buyer ant1 seller could make a contract The $325 buyer could buy from the $325 seller the $300 buyer could buy from the $300 seller and so forth wiihout violating any restrictions on the behavior of buyers and sellers Tntleed if we separately paired buyers and sellers in this special way each pair could be expectetl to make a bilateral contract a t the sellers miilimum price which ~voulti be equal to the buyers maximum price

I t should be noted that these e s ~ e r i - ments conform in several important ways to what we know must be true of many kinds of real markets In a real competi- tive market such as a commodity or stock exchange each marketer is likely to be ignorant of the reservation prices a t which other buyers and sellers are willing to trade Furthermore the only m y that a real marketer can obtain 1tiowletlge of market conditions is to

V n fact these schetlues are motiiiled as trading takes place Vhenevci- a ljuyer and a seller make a contract and drol) out of the market the demancl and supl)ly schetlules are shifted to the left in a nianner tlepentli~lg upon tlie buyers atid sellers position on the schetlules Iience the supply and tiemand ru~ictions co~itinually alter as the trading process occul-s I t is ~IiLhc~~it to imagine a real market ~xoccss which does not exhibit this characteristic Ihis means that the intra-trading-~~eriotl schedules are not iridepentlent of the transac~ions taking place FIo-ever the iiziiial schedules prevailirig a t the openilig of each trading period are independent of the transactions and it is these schedules that I identify with the theoretical conditions of supply and tlcmand which the theorist delines independ- ently of actual niarket prices and quantities One ol the importallt ol~jrctives in these experiments is to determine whether or not these irlitial schetlules have any power to ~)retlict the observetl behavior ol the market

observe the offers and bids that are ten- dered and whether or not they are ac- cepted These are the public data of the market A marketer can only know his own attitude and from observation learn something about the objective be- havior of others This is a major feature of these experimental markets We de- liberately avoid placing a t the disposal of our subjects any information which would not be practically attainable in a real market Each experimental market is forced to provide all of its own his- tory These markets are also a replica of real markets in that they are com-posed of a practical number of market- ers say twenty thirty or forty We do not require an indefinitely large number of marketers ~v l~ ich is usually supposed necessary for the existence of pure competition

One important condition operating in our experimental markets is not likely to prevail in real markets The experi- mental conditions of supply and demand are held constant over several successive trading periods in order to give any equilibrating mechanisms an opportuni- ty to establish an equilibrium over time Real markets are likely to be continu- ally subjected to changing conditions of supply and demand hlarshall was well aware of such problems and defined equi- librium as a condition toward which the market would move if the forces of sup- ply and demand were to remain station- ary for a sufficiently long time I t is this concept of equilibrium that this par- ticular series of experiments is designed in part to test There is nothing to prevent one from passing out new buyer andor seller cards representing changed demand andor supply conditions a t the end of each trading period if the objective is to study the effect of such constantly changing conditions on market behavior

In three of the nine experiments once- for-all changes in demand andor supply were made for purposes of studying the transient dynamics of a markets re-sponse to such stimuli

111 DESCRIPTION A h D DISCUSSION

OF E X P E R I M E N T A L RESULTS

The supply and demand schedule for each experiment is shown in the diagram on the left of Charts 1-10 The price and quantity a t which these schedules intersect will be referred to as the pre- dicted or theoretical equilibrium price and quantity for the corresponding ex- perimental market though such an equilibrium will not necessarily be attained or approached in the market The performance of each experimental market is summarized in the diagram on the right of Charts 1-10 and in Table 1 Each chart shows the sequence of contract or exchange prices in the order in which they occurred in each trading period Thus in Chart 1 the first transaction was effected a t $170 the second a t $180 and so on with a total of five transactions occurring in trading period 1 These charts show con- tract price as a function of transaction number rather than calendar time the latter of course being quite irrelevant to market dynamics

The most striking general characteris- tic of tests 1-3 5-7 9 and 10 is the remarkably strong tendency for exchange prices to approach the predicted equi- librium for each of these markets As the exchange process is repeated through successive trading periods with the same conditions of supply and demand pre- vailing initially in each period the varia- tion in exchange prices tends to decline and to cluster more closely around the equilibrium In Chart 1 for esample the variation in contract prices over the five

trading periods is from $170 to $225 The maximum possible variation is from $075 to $325 as seen in the supply and demand schedules As a means of measuring the convergence of exchange prices in each market a coefficient of convergence a has been coi~~puted for each trading period in each market The a for each trading period is the ratio of the standard deviation of exchange prices a to the predicted equilibriun~ price Po the ratio being expressed as a percentage That is a = 100 aolPo where a is the standard deviation of exchange prices around the equilibrium price rather than the mean exchange price Hence a provides a 111easure of exchange price variation relative to the predicted equilibrium exchange price is is seen in Table 1 and the charts for all tests except test 8 a tends to decline from one trading period to the next with tests 2 4A 5 6A 7 9A and 10 showing monotone convergence

Turning now to the individual experi- mental results it will be observed that the equilibrium price and quantity are approxin~ately the same for the supply and demand curves of tests 2 and 3 The significant difference in the design of these two tests is that the supply and demand schedules for test 2 are relatively flat while the corresponding schedules for test 3 are much more steep- ly inclined

Under the Walrasian hypothesis (the rate of increase in exchange price is an increasing function of the excess demand a t that price) one would expect the market in test 2 to converge more rapidly than that in test 3 As is evident from comparing the results in Charts 2 and 3 test 2 shows a more rapid and less er- ratic tendency toward equilibrium These results are of course cnnristent with many otller hypotheses including the

Irc- Coef- Ao of Sub Xo of SUE I clicted r~Luill ficient marginalAverage No of Sub- marginal s o of Sub-

Ex- Ex- of Con- H u q e ~ sActual marginal Sellers marginal clrdngc chaigc vergence n h oI ~ ~ ~ l ~ a n g c lloyers ho Sellers Qunn-

t i t y (30)

Quan-t i ty (XI

[a=

(100 un) (Po)I

Could AIaBc

Contractb

Price (r)

Who lade Coritracts

Could M a k e

Con t racts

Viio hladc Colltracts

---- -1-

1 6 5 5 6 3 5 6 5 5 6 7 5 6 6 5

15 16 4 15 15 4 15 16 4

16 17 5 16 5 16 5 16 3

10 None xone None Kone 10 None h-one xone None 10 None None Kone hTone 10 None Kone None None

8 None None None 8 None None None 8 None None None

10 10 10 10

12 12

12 None 12 Kone 12 hone 12 None

None None None None None None None hone Kone hone hTone None

xone None None None xone None

352 103 3 3 2

317 110 4 2 None None 336 3 2 4 1 None Kone 338 2 2 4 0 None None

CHART 2

0 2 4 6 8 10 12 14 16 18 20 2 2 1 4 8 12 17 4 8 12 15 4 O I 15 1 8 i 19

QUANTITY TRAN6ACTiC)N I 4 l i l G F i l I b Y P Rlgtl

excess-rent hypothesis to be discussed later7

The tests in Chart 4 are of special interest from the point of view of the Walrasian hypothesis In this case the supply curve is perfectly elastic-all sell-ers have cards containing the price $310 Each seller has the same lower bound on his reservation price acceptance set

equilibrium since there is a considerable excess supply a t prices just barely above the equilibrium price From the results we see that the market is not particularly slow in converging but i t converges to a fairly stable price about $020 above the predicted equilibrium Furthermore in test 4B which was an extension of 4A the interjection of a decrease in

CHART 4

TEST 4 A AND TEST 48 I6 C O I

- -- --- -580 -560 -5 4 0 - s

520 -

-5 00

Po 1310 Xo10

4 6 0 -

4 2 0 -u

2- 4 3 0 -+DECREASE

3 s o -

3 6 3 -

3 4 0

3 20

300

2 8 0

2 2 0 I

$ 6 0 0

5 80

560

5 4 0

5 2 0

5 0 0

4 80

460

4 4 0

4 20

IN DEMAYD+- O0

3 80

360

3 4 0

3 2 0

- 280

200 1 2 3 4 5 6 7 8 9 10 11 12 1 3 3 5 7 V I 3 5 7 V 1 3 5 7 9 1 3 5 7 9 1 3 5 7 8 1 3 5 7 1 3 5 6

Q ~ I A U T I T Y

In thi5 senie 11erc is no tlivergencc of attitude among the sellers though there might be marked variation in their bar- gaining propensities According to the Walrasian hypothesis this market should exhibit rapid convergence toward the

I T h e results are inconsistent n i t h the so-called hfarshallian hypothesis (the rate of increase in quan- tit) exchanged is an increasing function of the excess of demand price over supply price) but this hy- pothesis nould seem to be worth considering only in market processes in which some quantity-adjust- ing decision is made by the marketers The results of a pilot experiment in short-run and long-run equilibrium are displayed in the Appendix

TRANSACTION NUMBER ( B Y PERIOD1

demand from DD to DID was ineffective as a means of shocking the market down to its supply and demand equilibrium This decrease in demand was achieved by passing out new buyer cards corre- sponding to DD a t the close of period

in test 4A As the market approaches equilibrium from above since contracts a t prices below equilibrium are

The sellers in this market presented 3 solid front against price being lowered to ecluilibrium In the previous mar-

120 VERNON L SYIITFT

kets there was a divergence of seller attitude so that only a very few mar- ginal and near-marginal sellers might offer serious resistance to price being forced to equilibrium And this resistance tended to break down when any of the stronger intramarginal sellers accepted contracts below equilibrium

From these results it is clear that the static competitive market equilibri- um may depend not only on the inter- section of the supply and demanci sched- ules but also upon the shapes of the schedules Specifically I was led from test 4 to the tentative hypothesis that there may be an upward bias in the equilibrium price of a market which will be greater the more elastic is the supply schedule relative to demand8 For example let A be the area under the demand schedule and above the theoreti- cal equilibrium This is Alarshalls con-sumer surplus but to avoid any welfare connotations of this term I shall refer to the area as buyers rent Let B be the area above the supply schedule and below the theoretical equilibrium (Marshalls producer surplus) which I shall call sellers rent Now the tenta- tive hypothesis was that the actual mar- ket ecjuilibrium will be above the the- oretical equilibrium by an amount which depends upon how large A is relative to B Similarly there will be a downward bias if A is small relative to B

Test 4 is of course an extreme case since B = 0 In test 3 A is larger than B and the trading periods 3 and 4 ex-hibit a slight upward bias in the average actual exchange price (see Table 1) This provides some slight evidence in favor of the hypothesis

8 Note that the LValrasian hypothesis might lead one to expect a dol~nward bias since excess supply is very large at prices above equilihriuni if sup1)ly is very elastic relative to demand

As a consequence of these considera- tions test 7 was designed specifically to obtain additional information to sup- port or contradict the indicated hypothe- sis In this case as is seen in Chart 7 (see below) buyers rent is substan- tially smaller than sellers rent From the resulting course of contract prices over six trading periods in this experi- ment it is evident that the convergence to equilibrium is very slow From Table 1 the average exchange prices in the last three trading periods are respec- tively $332 $333 and $334 Average contract prices are still exhibiting a grad- ual approach to equilibrium Hence i t is entirely possible that the static equi- librium would eventually have been at- tained A still smaller buyers rent may be required to provide any clear down- ward bias in the static equilibrium One thing however seems quite unmistak- able from Chart 7 the relative magni- tude of buyers and sellers rent affects the speed with which the actual market equilibrium is approached One would expect sellers to present a somewhat weaker bargaining front especially a t first if their rent potential is large rela- tive to that of buyers Thus in Chart 7 i t is seen that several low reservation price sellers in trading periocls 1 and 2 made contracts a t low exchange prices which no doubt seemed quite profit- able to these sellers However in both these trading periods the later exchange prices were much higher revealing to the lour-price sellers that however prof- itable their initial sales had been still greater proLts were possible under stiffer bargaining

-4 stronger test of the hypotheses that buyer and seller rents affect the speed of adjustment and that they affect the final equil1rillln in the market would t)e ohtainal~lc l)j-introclucing actual mon-

etary payoffs in the experiment Thus one might offer to pay each seller the difference between his contract price and his reservation price and each buyer the difference between his reservation price and his contract price In addition one might pay each trader a small lump sum (say $005) just for making a contract in any period This sum would represent

GJeYTITi

iinormal pro~its that is a small return even if the good is sold a t its minimum supply price or purchased a t its maxi- mum demand price The present experi- ments have not seemeti to provide any motivation problems The subjects have shown high motivation to do their best even without monetary payo-tis But our experimental marginal buyers and sellers may be more reluctant to approach their reservation prices than their counter-parts in real markets The use oi nlone-tary payoifs as suggested should remox c

any such reluctance that is attributable to artificial elements in the present cx-peri i~lents ~

The experinlent summarized in Chart 5 was designed to study the effect on market behavior of changes in the condi- tions of demand and supply As it hap- pened this ex1)eriment was performed on a considerably more mature group

T R A N S A C T O N NJMBER ( 3 1 Pi11331

of subjects than any of the other experi- rnents Alost of the experiments were performed on sophornore ant1 junior en-gineering economics and business ma-jors while test 5 was performed on a

Since this was witten an experiment has been tried using monetary payofis and the same supply and demand design shown in Chart 4 The result as conjectured in the text TYas to remove the reluc- tance of sellers to sell at their reservation prices Ey the second trading period the market vas firmly in equilibrium In the thirtl period all trades were at $3ti) Al)parcntly$005 per pcriocl as considerecl satisfactory normal prolit

graduate class in econoinic theory 111

view of this dilference it is most interest- ing to find the phenomenally low values for a exhibited by test 5A The coefficient of convergence is smaller for the opening and later periods of this inarket than for any period of any of the other tests Furthermore trading periods 2-4 show as of less than 1 per cent indicating an inordinately strong and rapid tenden- cy toward equilibrium In this case no offers or bids were accepted until the bidding had converged to prices which were very near indeed to the ecluilibrium Contract prices ranged from $300 to S320 as compared with a possible range from $210 to $375

-It the close of test 5A new cards were distributed correspontling to an increase in demand from DD to DID as shown in Chart 51deg The subjects of course could guess from the fact that new buy- er cards were being distributed that a change in demand was in the wind But they knew nothing of the direction of change in demand except what might be guessed by the buyers from the al- teration of their individual reserv a t ion prices When trading began (period 1 test 5B) the immediate response was a very considerable upward sweep in exchange prices with several contracts being closed in the first trading period well above the new higher ecluilibrium price Indeed the eagerness to buy was so strong that two sellers who were submar- ginal both before and after the increase in demand (their reservation prices were

W o t e also that there was a small (one-unit) decrease in supply from SS to SS This was not planned It was due to the inal~ility of one sul~ject (the seller with the $210 reservation price) in test 5A to participate in test 5B Therefore except for the deletion of this one seller from the market the conditions of supply r e r e not altered that is the scllc~s ol test 5 B retni~~cclthe same rcscrvation 1)ricc cards as they liad ill test 51

$350 and $370) were able to m~bc con- tracts in this transient phase of the mar- ket Consecluently the trading group showing the strongest equilibrating ten- dencies exhibited very erratic behavior in the transient phase following the in- crease in demand Contract prices greatly overshot the new equilibrium and ration- ing by the market was less efficient in this transient phase In the second tratl- ing period of test 5B no submarginal sellers or buyers made contracts and tllc inarket exhibited a narrowed movcment toward the new equilibrium

Test 611 was designed to determine whether market equilibrium was affected by a marlred imbalance between the number of intramarginal sellers and the number of intramarginal buyers near the predicted equilibrium price The demand curve DD in Chart 6 falls continuously to the right in one-unit steps while the supply curve SS becomes perfectly in- elastic a t the price $400 well below the equilibrium price $1075 The tenta- tive hypothesis was that the large rent ($675) enjoyed by the marginal seller with still larger rents for the intramar- ginal sellers might prevent the theoreti- cal equilibrium from being established From the results it is seen that the earlier conjecture concerning the efiect of a divergence between buyer and seller rent on the approach to equilibrium is confirmed The approach to ecluilibrium is from below and the convergence is relatively slow However there is no indication that the lack of marginal sell- ers near the theoretical equilibrium has prevented the equilibrium from being attained The average contract price in trading period 4 is $1090 only $015 above the predicted equilibrium

4t the close of trading period 4 in test 611 thc old buyer cards correspond- ing to DD were rcplaced by new cards

correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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Page 3: An Experimental Study of Competitive Market Behavior Vernon L. …econ.ucsb.edu/~oprea/176/Competitive.pdf · 2007-09-26 · THE JOURNAL POLITICAL ECONOMY Volume LXX APRIL 1962 Number

Chamberlins paper was highly sugges- tive in demonstrating the potentialities of experimental techniques in the study of applied market theory

Parts I1 and I11 of this paper are devoted to a descriptive discussion of the experiments and some of their detailed results Parts IV and V present an em- pirical analysis of various equilibrating hypotheses and a rationalization of the hypothesis found to be most successful in these experiments

Part VI provides a brief summary which the reader may wish to consult before reading the main body of the paper

11 EXPERIMENTAL PROCEDURE

The experiments discussed in Parts I11 and IV have followed the same gen- eral design pattern The group of subjects is divided a t random into two subgroups a group of buyers and a group of sellers Each buyer receives a card containing a number known only to that buyer which represents the maximum price he is willing to pay for one unit of the fictitious commodity It is explained that the buyers are not to buy a unit of the commodity a t a price exceeding that appearing on their buyers card they would be quite happy to purchase a unit a t any price below this number-the lower the better but they would be entirely willing to pay just this price for the commodity rather than have their wants go unsatisfied I t is further ex-plained that each buyer should think of himself as making a pure pro6 t equal to the difference between his actual con- tract price and the maximum reserva- tion price on his card These reservation prices generate a demand curve such as DL) in the diagram on the left in Chart 1 At each price the correspond- ing quantity represents the maximum amount that could be purchased a t that

price Thus in Chart 1 the highest price buyer is willing to pay as much as $325 for one unit At a price above $325 the demand quantity is zero and a t $325 it cannot exceed one unit The next highest price buyer is willing to pay $300 Thus a t $300 the demand quantity cannot exceed two units The phrase cannot exceed rather than is will be seen to be of no small impor- tance How much is actually taken a t any price depends upon such important things as how the market is organized and various mechanical and bargaining considerations associated with the offer- acceptance process The demand curve therefore defines the set (all points on or to the left of DD) of possible demand quantities a t each strictly hypothetical ruling price

Each seller receives a card containing a number known only to that seller which represents the minimum price a t which he is willing to relinquish one unit of the commodity I t is explained that the sellers should be willing to sell a t their minimum supply price rather than fail to make a sale but they make a pure profit determined by the excess of their contract price over their mini- mum reservation price Under no con- dition should they sell below this mini- mum These minimum seller prices gen- erate a supply curve such as SS in Chart 1 At each hypothetical price the cor-responding quantity represents the maxi- mum amount that could be sold a t that price The supply curve therefore de- fines the set of possible supply quantities a t each hypothetical ruling price

In experiments 1-8 each buyer and seller is allowed to make a contract for the exchange of only a single unit of the commodity during any one trading or market period This rule was for the sake of simplicity and was relaxed in

EXPERIMENTAL STUDY OF COMPETITIVE MARKET BEHAVIOR 113

subsequent experiments Each experiment was conducted over

a sequence of trading periods five to ten minutes long depending upon the number of participants in the test group Since the experiments were conducted within a class period the number of trading periods was not uniform among

has been closed and the buyer and seller making the deal drop out of the market in the sense of no longer being permitted to make bids offers or contracts for the remainder of that market p e r i ~ d ~ As soon as a bid or offer is accepted the contract price is recorded together with the minimum supply price of the seller

CHART 1

TEST 1

the various experiments In the typical experiment the market opens for trad- ing period 1 This means that any buyer (or seller) is free a t any time to raise his hand and make a verbal offer to buy (or sell) a t any price which does not violate his maximum (or minimum) reservation price Thus in Chart 1 the buyer holding the $250 card might raise his hand and shout Buy a t $100 The seller with the $150 card might then shout Sell a t $360 Any seller (or buyer) is free to accept a bid (or offer) in which case a binding contract

and the maximum demand mice of the buyer involved in the transaition These observations represent the recorded data of the e~periment~ Within the time limit

All purchases are for final consumption There are no speculative purchases for resale in the same or later periods There is nothing however to pre- vent one from designing an experiment in which purchases for resale are permitted if the objective is to study the role of speculation in the equilibrating process One could for example permit the carry- over of s t d s from one period to the next

Owing to limitations of manpower and equip- ment in experiments 1-8 bids and offers which did not lead to transactions could not be recorded In subsequent experiments a tape recorder was used for this purpose

114 -ERNOX I SlITTII

of a trading period this procedure is continued until bids and ofters are no longer leading to contracts One or two calls are made for final bids or offers and the market is officially closed This ends period 1 The market is then im- mediately reopened for the second day of trading All buyers including those who did and those who did not make coiltracts in the preceding trading period i ~ o x ~ ~(as explained previously to the sub- jects) have a renewed urge to buy one unit of the commodity For each buyer the same maximum buying price holds in the second period as prevailed in the first period In this way the experimental demand curve represents a demand per unit time or per trading period Similarly each seller we may imagine has over- night acquired a fresh unit of the com- modity which he desires to sell in period 2 under the same minimum price con-ditions as prevailed in period 1 The experimental supply curve thereby repre- sents a willingness to supply per unit time Trading period 2 is allowed to run its course arlcl then period 3 and so on By this means we construct a prototype market in which there is a flow of a commodity onto and off the market The stage is thereby set to study price behavior under given conditions of nor- mal supply and demand5 Some buyers and sellers it should be noted may be unable to make contracts in any trading period or perhaps only in certain peri- ods Tnsofar as these traders are sub-marginal buyers or sellers this is to be eupected Indeed the ability of these experimental markets to ration out sub- marginal buyers and sellers will be one measure of the effectiveness or competi- tive performance of the market

The above design considerations define a rejection set of offers (and bids) for each I~uyer (and seller) which in turn

defines a demand and a supply schedule for the marliet in question-These sched- ules do nothing beyond setting extreme limits to the observable price-quantity behavior in that marliet All we can say is that the area above the supply curve is a region in which sales are feasible while tvhe area below the demand curve is a region in which purchases are feasi- ble ~ ~ m ~ e t i t i v e price theory asserts that there will be a tendency for price-quan- tity equilibrium to occur a t the extreme quantity point of the intersection of these G o areas For example in Chart 1 the shaded triangular area APB represents the intersection of these feasible sales and purchase sets with P the extreme point of this set We have no guarantee that the equilibrium defined by the inter- section of these sets will prevail even approximately in the experimental mar- ket (or any real counterpart of it) The mere fact that by any definition supply and demand schedules exist in the back- ground of a market does not guarantee that any meaningful relationship exists

The design of my experiments differs from that of Chamberlin (op cit) in several ways I n Chamber- lms experinlent the buyers and sellers simply cir- culate and engage in bilateral higgling and bargaining until they make a contract or the trading perioti ends As contracts are made the transaction price is recorded on the blackboard Consecluently there is very little if any multilateral bidding Each traders attention is directed to the one person with whom he is bargaining nhereas in my experiments each traders quotation is addressed to the entire trading group one quotation a t a time Also Cham- berlins experiment constitutes a pure exchange mar- ket operated for a single trading period There is therefore less opportunity for traders to gain experience and to modify their subsequent behavior in the light of such experience I t is only through some learning mechanism of this kind that I can imagine the possibility of equilibrium being ap-proached in any real market Finally in the present experiments I have varied the design from one experiment to another in a conscious attempt to study the effect of different conditions of supply and demand changes in supply or demand and changes in the rules of market organization on market-price behavior

ESPERIRlTSTL STTI)Y OF COLIPETITIIlt RI 4RKET BEH ITOR 115

between those schedules and what is ob- served in the market they are presumed to represent =11 the supply and demand schedules can do is set broad limits on the behavior of the market6 Thus in the symmetrical supply and demand dia- gram of Chart 3 it is conceivable that every buyer ant1 seller could make a contract The $325 buyer could buy from the $325 seller the $300 buyer could buy from the $300 seller and so forth wiihout violating any restrictions on the behavior of buyers and sellers Tntleed if we separately paired buyers and sellers in this special way each pair could be expectetl to make a bilateral contract a t the sellers miilimum price which ~voulti be equal to the buyers maximum price

I t should be noted that these e s ~ e r i - ments conform in several important ways to what we know must be true of many kinds of real markets In a real competi- tive market such as a commodity or stock exchange each marketer is likely to be ignorant of the reservation prices a t which other buyers and sellers are willing to trade Furthermore the only m y that a real marketer can obtain 1tiowletlge of market conditions is to

V n fact these schetlues are motiiiled as trading takes place Vhenevci- a ljuyer and a seller make a contract and drol) out of the market the demancl and supl)ly schetlules are shifted to the left in a nianner tlepentli~lg upon tlie buyers atid sellers position on the schetlules Iience the supply and tiemand ru~ictions co~itinually alter as the trading process occul-s I t is ~IiLhc~~it to imagine a real market ~xoccss which does not exhibit this characteristic Ihis means that the intra-trading-~~eriotl schedules are not iridepentlent of the transac~ions taking place FIo-ever the iiziiial schedules prevailirig a t the openilig of each trading period are independent of the transactions and it is these schedules that I identify with the theoretical conditions of supply and tlcmand which the theorist delines independ- ently of actual niarket prices and quantities One ol the importallt ol~jrctives in these experiments is to determine whether or not these irlitial schetlules have any power to ~)retlict the observetl behavior ol the market

observe the offers and bids that are ten- dered and whether or not they are ac- cepted These are the public data of the market A marketer can only know his own attitude and from observation learn something about the objective be- havior of others This is a major feature of these experimental markets We de- liberately avoid placing a t the disposal of our subjects any information which would not be practically attainable in a real market Each experimental market is forced to provide all of its own his- tory These markets are also a replica of real markets in that they are com-posed of a practical number of market- ers say twenty thirty or forty We do not require an indefinitely large number of marketers ~v l~ ich is usually supposed necessary for the existence of pure competition

One important condition operating in our experimental markets is not likely to prevail in real markets The experi- mental conditions of supply and demand are held constant over several successive trading periods in order to give any equilibrating mechanisms an opportuni- ty to establish an equilibrium over time Real markets are likely to be continu- ally subjected to changing conditions of supply and demand hlarshall was well aware of such problems and defined equi- librium as a condition toward which the market would move if the forces of sup- ply and demand were to remain station- ary for a sufficiently long time I t is this concept of equilibrium that this par- ticular series of experiments is designed in part to test There is nothing to prevent one from passing out new buyer andor seller cards representing changed demand andor supply conditions a t the end of each trading period if the objective is to study the effect of such constantly changing conditions on market behavior

In three of the nine experiments once- for-all changes in demand andor supply were made for purposes of studying the transient dynamics of a markets re-sponse to such stimuli

111 DESCRIPTION A h D DISCUSSION

OF E X P E R I M E N T A L RESULTS

The supply and demand schedule for each experiment is shown in the diagram on the left of Charts 1-10 The price and quantity a t which these schedules intersect will be referred to as the pre- dicted or theoretical equilibrium price and quantity for the corresponding ex- perimental market though such an equilibrium will not necessarily be attained or approached in the market The performance of each experimental market is summarized in the diagram on the right of Charts 1-10 and in Table 1 Each chart shows the sequence of contract or exchange prices in the order in which they occurred in each trading period Thus in Chart 1 the first transaction was effected a t $170 the second a t $180 and so on with a total of five transactions occurring in trading period 1 These charts show con- tract price as a function of transaction number rather than calendar time the latter of course being quite irrelevant to market dynamics

The most striking general characteris- tic of tests 1-3 5-7 9 and 10 is the remarkably strong tendency for exchange prices to approach the predicted equi- librium for each of these markets As the exchange process is repeated through successive trading periods with the same conditions of supply and demand pre- vailing initially in each period the varia- tion in exchange prices tends to decline and to cluster more closely around the equilibrium In Chart 1 for esample the variation in contract prices over the five

trading periods is from $170 to $225 The maximum possible variation is from $075 to $325 as seen in the supply and demand schedules As a means of measuring the convergence of exchange prices in each market a coefficient of convergence a has been coi~~puted for each trading period in each market The a for each trading period is the ratio of the standard deviation of exchange prices a to the predicted equilibriun~ price Po the ratio being expressed as a percentage That is a = 100 aolPo where a is the standard deviation of exchange prices around the equilibrium price rather than the mean exchange price Hence a provides a 111easure of exchange price variation relative to the predicted equilibrium exchange price is is seen in Table 1 and the charts for all tests except test 8 a tends to decline from one trading period to the next with tests 2 4A 5 6A 7 9A and 10 showing monotone convergence

Turning now to the individual experi- mental results it will be observed that the equilibrium price and quantity are approxin~ately the same for the supply and demand curves of tests 2 and 3 The significant difference in the design of these two tests is that the supply and demand schedules for test 2 are relatively flat while the corresponding schedules for test 3 are much more steep- ly inclined

Under the Walrasian hypothesis (the rate of increase in exchange price is an increasing function of the excess demand a t that price) one would expect the market in test 2 to converge more rapidly than that in test 3 As is evident from comparing the results in Charts 2 and 3 test 2 shows a more rapid and less er- ratic tendency toward equilibrium These results are of course cnnristent with many otller hypotheses including the

Irc- Coef- Ao of Sub Xo of SUE I clicted r~Luill ficient marginalAverage No of Sub- marginal s o of Sub-

Ex- Ex- of Con- H u q e ~ sActual marginal Sellers marginal clrdngc chaigc vergence n h oI ~ ~ ~ l ~ a n g c lloyers ho Sellers Qunn-

t i t y (30)

Quan-t i ty (XI

[a=

(100 un) (Po)I

Could AIaBc

Contractb

Price (r)

Who lade Coritracts

Could M a k e

Con t racts

Viio hladc Colltracts

---- -1-

1 6 5 5 6 3 5 6 5 5 6 7 5 6 6 5

15 16 4 15 15 4 15 16 4

16 17 5 16 5 16 5 16 3

10 None xone None Kone 10 None h-one xone None 10 None None Kone hTone 10 None Kone None None

8 None None None 8 None None None 8 None None None

10 10 10 10

12 12

12 None 12 Kone 12 hone 12 None

None None None None None None None hone Kone hone hTone None

xone None None None xone None

352 103 3 3 2

317 110 4 2 None None 336 3 2 4 1 None Kone 338 2 2 4 0 None None

CHART 2

0 2 4 6 8 10 12 14 16 18 20 2 2 1 4 8 12 17 4 8 12 15 4 O I 15 1 8 i 19

QUANTITY TRAN6ACTiC)N I 4 l i l G F i l I b Y P Rlgtl

excess-rent hypothesis to be discussed later7

The tests in Chart 4 are of special interest from the point of view of the Walrasian hypothesis In this case the supply curve is perfectly elastic-all sell-ers have cards containing the price $310 Each seller has the same lower bound on his reservation price acceptance set

equilibrium since there is a considerable excess supply a t prices just barely above the equilibrium price From the results we see that the market is not particularly slow in converging but i t converges to a fairly stable price about $020 above the predicted equilibrium Furthermore in test 4B which was an extension of 4A the interjection of a decrease in

CHART 4

TEST 4 A AND TEST 48 I6 C O I

- -- --- -580 -560 -5 4 0 - s

520 -

-5 00

Po 1310 Xo10

4 6 0 -

4 2 0 -u

2- 4 3 0 -+DECREASE

3 s o -

3 6 3 -

3 4 0

3 20

300

2 8 0

2 2 0 I

$ 6 0 0

5 80

560

5 4 0

5 2 0

5 0 0

4 80

460

4 4 0

4 20

IN DEMAYD+- O0

3 80

360

3 4 0

3 2 0

- 280

200 1 2 3 4 5 6 7 8 9 10 11 12 1 3 3 5 7 V I 3 5 7 V 1 3 5 7 9 1 3 5 7 9 1 3 5 7 8 1 3 5 7 1 3 5 6

Q ~ I A U T I T Y

In thi5 senie 11erc is no tlivergencc of attitude among the sellers though there might be marked variation in their bar- gaining propensities According to the Walrasian hypothesis this market should exhibit rapid convergence toward the

I T h e results are inconsistent n i t h the so-called hfarshallian hypothesis (the rate of increase in quan- tit) exchanged is an increasing function of the excess of demand price over supply price) but this hy- pothesis nould seem to be worth considering only in market processes in which some quantity-adjust- ing decision is made by the marketers The results of a pilot experiment in short-run and long-run equilibrium are displayed in the Appendix

TRANSACTION NUMBER ( B Y PERIOD1

demand from DD to DID was ineffective as a means of shocking the market down to its supply and demand equilibrium This decrease in demand was achieved by passing out new buyer cards corre- sponding to DD a t the close of period

in test 4A As the market approaches equilibrium from above since contracts a t prices below equilibrium are

The sellers in this market presented 3 solid front against price being lowered to ecluilibrium In the previous mar-

120 VERNON L SYIITFT

kets there was a divergence of seller attitude so that only a very few mar- ginal and near-marginal sellers might offer serious resistance to price being forced to equilibrium And this resistance tended to break down when any of the stronger intramarginal sellers accepted contracts below equilibrium

From these results it is clear that the static competitive market equilibri- um may depend not only on the inter- section of the supply and demanci sched- ules but also upon the shapes of the schedules Specifically I was led from test 4 to the tentative hypothesis that there may be an upward bias in the equilibrium price of a market which will be greater the more elastic is the supply schedule relative to demand8 For example let A be the area under the demand schedule and above the theoreti- cal equilibrium This is Alarshalls con-sumer surplus but to avoid any welfare connotations of this term I shall refer to the area as buyers rent Let B be the area above the supply schedule and below the theoretical equilibrium (Marshalls producer surplus) which I shall call sellers rent Now the tenta- tive hypothesis was that the actual mar- ket ecjuilibrium will be above the the- oretical equilibrium by an amount which depends upon how large A is relative to B Similarly there will be a downward bias if A is small relative to B

Test 4 is of course an extreme case since B = 0 In test 3 A is larger than B and the trading periods 3 and 4 ex-hibit a slight upward bias in the average actual exchange price (see Table 1) This provides some slight evidence in favor of the hypothesis

8 Note that the LValrasian hypothesis might lead one to expect a dol~nward bias since excess supply is very large at prices above equilihriuni if sup1)ly is very elastic relative to demand

As a consequence of these considera- tions test 7 was designed specifically to obtain additional information to sup- port or contradict the indicated hypothe- sis In this case as is seen in Chart 7 (see below) buyers rent is substan- tially smaller than sellers rent From the resulting course of contract prices over six trading periods in this experi- ment it is evident that the convergence to equilibrium is very slow From Table 1 the average exchange prices in the last three trading periods are respec- tively $332 $333 and $334 Average contract prices are still exhibiting a grad- ual approach to equilibrium Hence i t is entirely possible that the static equi- librium would eventually have been at- tained A still smaller buyers rent may be required to provide any clear down- ward bias in the static equilibrium One thing however seems quite unmistak- able from Chart 7 the relative magni- tude of buyers and sellers rent affects the speed with which the actual market equilibrium is approached One would expect sellers to present a somewhat weaker bargaining front especially a t first if their rent potential is large rela- tive to that of buyers Thus in Chart 7 i t is seen that several low reservation price sellers in trading periocls 1 and 2 made contracts a t low exchange prices which no doubt seemed quite profit- able to these sellers However in both these trading periods the later exchange prices were much higher revealing to the lour-price sellers that however prof- itable their initial sales had been still greater proLts were possible under stiffer bargaining

-4 stronger test of the hypotheses that buyer and seller rents affect the speed of adjustment and that they affect the final equil1rillln in the market would t)e ohtainal~lc l)j-introclucing actual mon-

etary payoffs in the experiment Thus one might offer to pay each seller the difference between his contract price and his reservation price and each buyer the difference between his reservation price and his contract price In addition one might pay each trader a small lump sum (say $005) just for making a contract in any period This sum would represent

GJeYTITi

iinormal pro~its that is a small return even if the good is sold a t its minimum supply price or purchased a t its maxi- mum demand price The present experi- ments have not seemeti to provide any motivation problems The subjects have shown high motivation to do their best even without monetary payo-tis But our experimental marginal buyers and sellers may be more reluctant to approach their reservation prices than their counter-parts in real markets The use oi nlone-tary payoifs as suggested should remox c

any such reluctance that is attributable to artificial elements in the present cx-peri i~lents ~

The experinlent summarized in Chart 5 was designed to study the effect on market behavior of changes in the condi- tions of demand and supply As it hap- pened this ex1)eriment was performed on a considerably more mature group

T R A N S A C T O N NJMBER ( 3 1 Pi11331

of subjects than any of the other experi- rnents Alost of the experiments were performed on sophornore ant1 junior en-gineering economics and business ma-jors while test 5 was performed on a

Since this was witten an experiment has been tried using monetary payofis and the same supply and demand design shown in Chart 4 The result as conjectured in the text TYas to remove the reluc- tance of sellers to sell at their reservation prices Ey the second trading period the market vas firmly in equilibrium In the thirtl period all trades were at $3ti) Al)parcntly$005 per pcriocl as considerecl satisfactory normal prolit

graduate class in econoinic theory 111

view of this dilference it is most interest- ing to find the phenomenally low values for a exhibited by test 5A The coefficient of convergence is smaller for the opening and later periods of this inarket than for any period of any of the other tests Furthermore trading periods 2-4 show as of less than 1 per cent indicating an inordinately strong and rapid tenden- cy toward equilibrium In this case no offers or bids were accepted until the bidding had converged to prices which were very near indeed to the ecluilibrium Contract prices ranged from $300 to S320 as compared with a possible range from $210 to $375

-It the close of test 5A new cards were distributed correspontling to an increase in demand from DD to DID as shown in Chart 51deg The subjects of course could guess from the fact that new buy- er cards were being distributed that a change in demand was in the wind But they knew nothing of the direction of change in demand except what might be guessed by the buyers from the al- teration of their individual reserv a t ion prices When trading began (period 1 test 5B) the immediate response was a very considerable upward sweep in exchange prices with several contracts being closed in the first trading period well above the new higher ecluilibrium price Indeed the eagerness to buy was so strong that two sellers who were submar- ginal both before and after the increase in demand (their reservation prices were

W o t e also that there was a small (one-unit) decrease in supply from SS to SS This was not planned It was due to the inal~ility of one sul~ject (the seller with the $210 reservation price) in test 5A to participate in test 5B Therefore except for the deletion of this one seller from the market the conditions of supply r e r e not altered that is the scllc~s ol test 5 B retni~~cclthe same rcscrvation 1)ricc cards as they liad ill test 51

$350 and $370) were able to m~bc con- tracts in this transient phase of the mar- ket Consecluently the trading group showing the strongest equilibrating ten- dencies exhibited very erratic behavior in the transient phase following the in- crease in demand Contract prices greatly overshot the new equilibrium and ration- ing by the market was less efficient in this transient phase In the second tratl- ing period of test 5B no submarginal sellers or buyers made contracts and tllc inarket exhibited a narrowed movcment toward the new equilibrium

Test 611 was designed to determine whether market equilibrium was affected by a marlred imbalance between the number of intramarginal sellers and the number of intramarginal buyers near the predicted equilibrium price The demand curve DD in Chart 6 falls continuously to the right in one-unit steps while the supply curve SS becomes perfectly in- elastic a t the price $400 well below the equilibrium price $1075 The tenta- tive hypothesis was that the large rent ($675) enjoyed by the marginal seller with still larger rents for the intramar- ginal sellers might prevent the theoreti- cal equilibrium from being established From the results it is seen that the earlier conjecture concerning the efiect of a divergence between buyer and seller rent on the approach to equilibrium is confirmed The approach to ecluilibrium is from below and the convergence is relatively slow However there is no indication that the lack of marginal sell- ers near the theoretical equilibrium has prevented the equilibrium from being attained The average contract price in trading period 4 is $1090 only $015 above the predicted equilibrium

4t the close of trading period 4 in test 611 thc old buyer cards correspond- ing to DD were rcplaced by new cards

correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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EXPERIMENTAL STUDY OF COMPETITIVE MARKET BEHAVIOR 113

subsequent experiments Each experiment was conducted over

a sequence of trading periods five to ten minutes long depending upon the number of participants in the test group Since the experiments were conducted within a class period the number of trading periods was not uniform among

has been closed and the buyer and seller making the deal drop out of the market in the sense of no longer being permitted to make bids offers or contracts for the remainder of that market p e r i ~ d ~ As soon as a bid or offer is accepted the contract price is recorded together with the minimum supply price of the seller

CHART 1

TEST 1

the various experiments In the typical experiment the market opens for trad- ing period 1 This means that any buyer (or seller) is free a t any time to raise his hand and make a verbal offer to buy (or sell) a t any price which does not violate his maximum (or minimum) reservation price Thus in Chart 1 the buyer holding the $250 card might raise his hand and shout Buy a t $100 The seller with the $150 card might then shout Sell a t $360 Any seller (or buyer) is free to accept a bid (or offer) in which case a binding contract

and the maximum demand mice of the buyer involved in the transaition These observations represent the recorded data of the e~periment~ Within the time limit

All purchases are for final consumption There are no speculative purchases for resale in the same or later periods There is nothing however to pre- vent one from designing an experiment in which purchases for resale are permitted if the objective is to study the role of speculation in the equilibrating process One could for example permit the carry- over of s t d s from one period to the next

Owing to limitations of manpower and equip- ment in experiments 1-8 bids and offers which did not lead to transactions could not be recorded In subsequent experiments a tape recorder was used for this purpose

114 -ERNOX I SlITTII

of a trading period this procedure is continued until bids and ofters are no longer leading to contracts One or two calls are made for final bids or offers and the market is officially closed This ends period 1 The market is then im- mediately reopened for the second day of trading All buyers including those who did and those who did not make coiltracts in the preceding trading period i ~ o x ~ ~(as explained previously to the sub- jects) have a renewed urge to buy one unit of the commodity For each buyer the same maximum buying price holds in the second period as prevailed in the first period In this way the experimental demand curve represents a demand per unit time or per trading period Similarly each seller we may imagine has over- night acquired a fresh unit of the com- modity which he desires to sell in period 2 under the same minimum price con-ditions as prevailed in period 1 The experimental supply curve thereby repre- sents a willingness to supply per unit time Trading period 2 is allowed to run its course arlcl then period 3 and so on By this means we construct a prototype market in which there is a flow of a commodity onto and off the market The stage is thereby set to study price behavior under given conditions of nor- mal supply and demand5 Some buyers and sellers it should be noted may be unable to make contracts in any trading period or perhaps only in certain peri- ods Tnsofar as these traders are sub-marginal buyers or sellers this is to be eupected Indeed the ability of these experimental markets to ration out sub- marginal buyers and sellers will be one measure of the effectiveness or competi- tive performance of the market

The above design considerations define a rejection set of offers (and bids) for each I~uyer (and seller) which in turn

defines a demand and a supply schedule for the marliet in question-These sched- ules do nothing beyond setting extreme limits to the observable price-quantity behavior in that marliet All we can say is that the area above the supply curve is a region in which sales are feasible while tvhe area below the demand curve is a region in which purchases are feasi- ble ~ ~ m ~ e t i t i v e price theory asserts that there will be a tendency for price-quan- tity equilibrium to occur a t the extreme quantity point of the intersection of these G o areas For example in Chart 1 the shaded triangular area APB represents the intersection of these feasible sales and purchase sets with P the extreme point of this set We have no guarantee that the equilibrium defined by the inter- section of these sets will prevail even approximately in the experimental mar- ket (or any real counterpart of it) The mere fact that by any definition supply and demand schedules exist in the back- ground of a market does not guarantee that any meaningful relationship exists

The design of my experiments differs from that of Chamberlin (op cit) in several ways I n Chamber- lms experinlent the buyers and sellers simply cir- culate and engage in bilateral higgling and bargaining until they make a contract or the trading perioti ends As contracts are made the transaction price is recorded on the blackboard Consecluently there is very little if any multilateral bidding Each traders attention is directed to the one person with whom he is bargaining nhereas in my experiments each traders quotation is addressed to the entire trading group one quotation a t a time Also Cham- berlins experiment constitutes a pure exchange mar- ket operated for a single trading period There is therefore less opportunity for traders to gain experience and to modify their subsequent behavior in the light of such experience I t is only through some learning mechanism of this kind that I can imagine the possibility of equilibrium being ap-proached in any real market Finally in the present experiments I have varied the design from one experiment to another in a conscious attempt to study the effect of different conditions of supply and demand changes in supply or demand and changes in the rules of market organization on market-price behavior

ESPERIRlTSTL STTI)Y OF COLIPETITIIlt RI 4RKET BEH ITOR 115

between those schedules and what is ob- served in the market they are presumed to represent =11 the supply and demand schedules can do is set broad limits on the behavior of the market6 Thus in the symmetrical supply and demand dia- gram of Chart 3 it is conceivable that every buyer ant1 seller could make a contract The $325 buyer could buy from the $325 seller the $300 buyer could buy from the $300 seller and so forth wiihout violating any restrictions on the behavior of buyers and sellers Tntleed if we separately paired buyers and sellers in this special way each pair could be expectetl to make a bilateral contract a t the sellers miilimum price which ~voulti be equal to the buyers maximum price

I t should be noted that these e s ~ e r i - ments conform in several important ways to what we know must be true of many kinds of real markets In a real competi- tive market such as a commodity or stock exchange each marketer is likely to be ignorant of the reservation prices a t which other buyers and sellers are willing to trade Furthermore the only m y that a real marketer can obtain 1tiowletlge of market conditions is to

V n fact these schetlues are motiiiled as trading takes place Vhenevci- a ljuyer and a seller make a contract and drol) out of the market the demancl and supl)ly schetlules are shifted to the left in a nianner tlepentli~lg upon tlie buyers atid sellers position on the schetlules Iience the supply and tiemand ru~ictions co~itinually alter as the trading process occul-s I t is ~IiLhc~~it to imagine a real market ~xoccss which does not exhibit this characteristic Ihis means that the intra-trading-~~eriotl schedules are not iridepentlent of the transac~ions taking place FIo-ever the iiziiial schedules prevailirig a t the openilig of each trading period are independent of the transactions and it is these schedules that I identify with the theoretical conditions of supply and tlcmand which the theorist delines independ- ently of actual niarket prices and quantities One ol the importallt ol~jrctives in these experiments is to determine whether or not these irlitial schetlules have any power to ~)retlict the observetl behavior ol the market

observe the offers and bids that are ten- dered and whether or not they are ac- cepted These are the public data of the market A marketer can only know his own attitude and from observation learn something about the objective be- havior of others This is a major feature of these experimental markets We de- liberately avoid placing a t the disposal of our subjects any information which would not be practically attainable in a real market Each experimental market is forced to provide all of its own his- tory These markets are also a replica of real markets in that they are com-posed of a practical number of market- ers say twenty thirty or forty We do not require an indefinitely large number of marketers ~v l~ ich is usually supposed necessary for the existence of pure competition

One important condition operating in our experimental markets is not likely to prevail in real markets The experi- mental conditions of supply and demand are held constant over several successive trading periods in order to give any equilibrating mechanisms an opportuni- ty to establish an equilibrium over time Real markets are likely to be continu- ally subjected to changing conditions of supply and demand hlarshall was well aware of such problems and defined equi- librium as a condition toward which the market would move if the forces of sup- ply and demand were to remain station- ary for a sufficiently long time I t is this concept of equilibrium that this par- ticular series of experiments is designed in part to test There is nothing to prevent one from passing out new buyer andor seller cards representing changed demand andor supply conditions a t the end of each trading period if the objective is to study the effect of such constantly changing conditions on market behavior

In three of the nine experiments once- for-all changes in demand andor supply were made for purposes of studying the transient dynamics of a markets re-sponse to such stimuli

111 DESCRIPTION A h D DISCUSSION

OF E X P E R I M E N T A L RESULTS

The supply and demand schedule for each experiment is shown in the diagram on the left of Charts 1-10 The price and quantity a t which these schedules intersect will be referred to as the pre- dicted or theoretical equilibrium price and quantity for the corresponding ex- perimental market though such an equilibrium will not necessarily be attained or approached in the market The performance of each experimental market is summarized in the diagram on the right of Charts 1-10 and in Table 1 Each chart shows the sequence of contract or exchange prices in the order in which they occurred in each trading period Thus in Chart 1 the first transaction was effected a t $170 the second a t $180 and so on with a total of five transactions occurring in trading period 1 These charts show con- tract price as a function of transaction number rather than calendar time the latter of course being quite irrelevant to market dynamics

The most striking general characteris- tic of tests 1-3 5-7 9 and 10 is the remarkably strong tendency for exchange prices to approach the predicted equi- librium for each of these markets As the exchange process is repeated through successive trading periods with the same conditions of supply and demand pre- vailing initially in each period the varia- tion in exchange prices tends to decline and to cluster more closely around the equilibrium In Chart 1 for esample the variation in contract prices over the five

trading periods is from $170 to $225 The maximum possible variation is from $075 to $325 as seen in the supply and demand schedules As a means of measuring the convergence of exchange prices in each market a coefficient of convergence a has been coi~~puted for each trading period in each market The a for each trading period is the ratio of the standard deviation of exchange prices a to the predicted equilibriun~ price Po the ratio being expressed as a percentage That is a = 100 aolPo where a is the standard deviation of exchange prices around the equilibrium price rather than the mean exchange price Hence a provides a 111easure of exchange price variation relative to the predicted equilibrium exchange price is is seen in Table 1 and the charts for all tests except test 8 a tends to decline from one trading period to the next with tests 2 4A 5 6A 7 9A and 10 showing monotone convergence

Turning now to the individual experi- mental results it will be observed that the equilibrium price and quantity are approxin~ately the same for the supply and demand curves of tests 2 and 3 The significant difference in the design of these two tests is that the supply and demand schedules for test 2 are relatively flat while the corresponding schedules for test 3 are much more steep- ly inclined

Under the Walrasian hypothesis (the rate of increase in exchange price is an increasing function of the excess demand a t that price) one would expect the market in test 2 to converge more rapidly than that in test 3 As is evident from comparing the results in Charts 2 and 3 test 2 shows a more rapid and less er- ratic tendency toward equilibrium These results are of course cnnristent with many otller hypotheses including the

Irc- Coef- Ao of Sub Xo of SUE I clicted r~Luill ficient marginalAverage No of Sub- marginal s o of Sub-

Ex- Ex- of Con- H u q e ~ sActual marginal Sellers marginal clrdngc chaigc vergence n h oI ~ ~ ~ l ~ a n g c lloyers ho Sellers Qunn-

t i t y (30)

Quan-t i ty (XI

[a=

(100 un) (Po)I

Could AIaBc

Contractb

Price (r)

Who lade Coritracts

Could M a k e

Con t racts

Viio hladc Colltracts

---- -1-

1 6 5 5 6 3 5 6 5 5 6 7 5 6 6 5

15 16 4 15 15 4 15 16 4

16 17 5 16 5 16 5 16 3

10 None xone None Kone 10 None h-one xone None 10 None None Kone hTone 10 None Kone None None

8 None None None 8 None None None 8 None None None

10 10 10 10

12 12

12 None 12 Kone 12 hone 12 None

None None None None None None None hone Kone hone hTone None

xone None None None xone None

352 103 3 3 2

317 110 4 2 None None 336 3 2 4 1 None Kone 338 2 2 4 0 None None

CHART 2

0 2 4 6 8 10 12 14 16 18 20 2 2 1 4 8 12 17 4 8 12 15 4 O I 15 1 8 i 19

QUANTITY TRAN6ACTiC)N I 4 l i l G F i l I b Y P Rlgtl

excess-rent hypothesis to be discussed later7

The tests in Chart 4 are of special interest from the point of view of the Walrasian hypothesis In this case the supply curve is perfectly elastic-all sell-ers have cards containing the price $310 Each seller has the same lower bound on his reservation price acceptance set

equilibrium since there is a considerable excess supply a t prices just barely above the equilibrium price From the results we see that the market is not particularly slow in converging but i t converges to a fairly stable price about $020 above the predicted equilibrium Furthermore in test 4B which was an extension of 4A the interjection of a decrease in

CHART 4

TEST 4 A AND TEST 48 I6 C O I

- -- --- -580 -560 -5 4 0 - s

520 -

-5 00

Po 1310 Xo10

4 6 0 -

4 2 0 -u

2- 4 3 0 -+DECREASE

3 s o -

3 6 3 -

3 4 0

3 20

300

2 8 0

2 2 0 I

$ 6 0 0

5 80

560

5 4 0

5 2 0

5 0 0

4 80

460

4 4 0

4 20

IN DEMAYD+- O0

3 80

360

3 4 0

3 2 0

- 280

200 1 2 3 4 5 6 7 8 9 10 11 12 1 3 3 5 7 V I 3 5 7 V 1 3 5 7 9 1 3 5 7 9 1 3 5 7 8 1 3 5 7 1 3 5 6

Q ~ I A U T I T Y

In thi5 senie 11erc is no tlivergencc of attitude among the sellers though there might be marked variation in their bar- gaining propensities According to the Walrasian hypothesis this market should exhibit rapid convergence toward the

I T h e results are inconsistent n i t h the so-called hfarshallian hypothesis (the rate of increase in quan- tit) exchanged is an increasing function of the excess of demand price over supply price) but this hy- pothesis nould seem to be worth considering only in market processes in which some quantity-adjust- ing decision is made by the marketers The results of a pilot experiment in short-run and long-run equilibrium are displayed in the Appendix

TRANSACTION NUMBER ( B Y PERIOD1

demand from DD to DID was ineffective as a means of shocking the market down to its supply and demand equilibrium This decrease in demand was achieved by passing out new buyer cards corre- sponding to DD a t the close of period

in test 4A As the market approaches equilibrium from above since contracts a t prices below equilibrium are

The sellers in this market presented 3 solid front against price being lowered to ecluilibrium In the previous mar-

120 VERNON L SYIITFT

kets there was a divergence of seller attitude so that only a very few mar- ginal and near-marginal sellers might offer serious resistance to price being forced to equilibrium And this resistance tended to break down when any of the stronger intramarginal sellers accepted contracts below equilibrium

From these results it is clear that the static competitive market equilibri- um may depend not only on the inter- section of the supply and demanci sched- ules but also upon the shapes of the schedules Specifically I was led from test 4 to the tentative hypothesis that there may be an upward bias in the equilibrium price of a market which will be greater the more elastic is the supply schedule relative to demand8 For example let A be the area under the demand schedule and above the theoreti- cal equilibrium This is Alarshalls con-sumer surplus but to avoid any welfare connotations of this term I shall refer to the area as buyers rent Let B be the area above the supply schedule and below the theoretical equilibrium (Marshalls producer surplus) which I shall call sellers rent Now the tenta- tive hypothesis was that the actual mar- ket ecjuilibrium will be above the the- oretical equilibrium by an amount which depends upon how large A is relative to B Similarly there will be a downward bias if A is small relative to B

Test 4 is of course an extreme case since B = 0 In test 3 A is larger than B and the trading periods 3 and 4 ex-hibit a slight upward bias in the average actual exchange price (see Table 1) This provides some slight evidence in favor of the hypothesis

8 Note that the LValrasian hypothesis might lead one to expect a dol~nward bias since excess supply is very large at prices above equilihriuni if sup1)ly is very elastic relative to demand

As a consequence of these considera- tions test 7 was designed specifically to obtain additional information to sup- port or contradict the indicated hypothe- sis In this case as is seen in Chart 7 (see below) buyers rent is substan- tially smaller than sellers rent From the resulting course of contract prices over six trading periods in this experi- ment it is evident that the convergence to equilibrium is very slow From Table 1 the average exchange prices in the last three trading periods are respec- tively $332 $333 and $334 Average contract prices are still exhibiting a grad- ual approach to equilibrium Hence i t is entirely possible that the static equi- librium would eventually have been at- tained A still smaller buyers rent may be required to provide any clear down- ward bias in the static equilibrium One thing however seems quite unmistak- able from Chart 7 the relative magni- tude of buyers and sellers rent affects the speed with which the actual market equilibrium is approached One would expect sellers to present a somewhat weaker bargaining front especially a t first if their rent potential is large rela- tive to that of buyers Thus in Chart 7 i t is seen that several low reservation price sellers in trading periocls 1 and 2 made contracts a t low exchange prices which no doubt seemed quite profit- able to these sellers However in both these trading periods the later exchange prices were much higher revealing to the lour-price sellers that however prof- itable their initial sales had been still greater proLts were possible under stiffer bargaining

-4 stronger test of the hypotheses that buyer and seller rents affect the speed of adjustment and that they affect the final equil1rillln in the market would t)e ohtainal~lc l)j-introclucing actual mon-

etary payoffs in the experiment Thus one might offer to pay each seller the difference between his contract price and his reservation price and each buyer the difference between his reservation price and his contract price In addition one might pay each trader a small lump sum (say $005) just for making a contract in any period This sum would represent

GJeYTITi

iinormal pro~its that is a small return even if the good is sold a t its minimum supply price or purchased a t its maxi- mum demand price The present experi- ments have not seemeti to provide any motivation problems The subjects have shown high motivation to do their best even without monetary payo-tis But our experimental marginal buyers and sellers may be more reluctant to approach their reservation prices than their counter-parts in real markets The use oi nlone-tary payoifs as suggested should remox c

any such reluctance that is attributable to artificial elements in the present cx-peri i~lents ~

The experinlent summarized in Chart 5 was designed to study the effect on market behavior of changes in the condi- tions of demand and supply As it hap- pened this ex1)eriment was performed on a considerably more mature group

T R A N S A C T O N NJMBER ( 3 1 Pi11331

of subjects than any of the other experi- rnents Alost of the experiments were performed on sophornore ant1 junior en-gineering economics and business ma-jors while test 5 was performed on a

Since this was witten an experiment has been tried using monetary payofis and the same supply and demand design shown in Chart 4 The result as conjectured in the text TYas to remove the reluc- tance of sellers to sell at their reservation prices Ey the second trading period the market vas firmly in equilibrium In the thirtl period all trades were at $3ti) Al)parcntly$005 per pcriocl as considerecl satisfactory normal prolit

graduate class in econoinic theory 111

view of this dilference it is most interest- ing to find the phenomenally low values for a exhibited by test 5A The coefficient of convergence is smaller for the opening and later periods of this inarket than for any period of any of the other tests Furthermore trading periods 2-4 show as of less than 1 per cent indicating an inordinately strong and rapid tenden- cy toward equilibrium In this case no offers or bids were accepted until the bidding had converged to prices which were very near indeed to the ecluilibrium Contract prices ranged from $300 to S320 as compared with a possible range from $210 to $375

-It the close of test 5A new cards were distributed correspontling to an increase in demand from DD to DID as shown in Chart 51deg The subjects of course could guess from the fact that new buy- er cards were being distributed that a change in demand was in the wind But they knew nothing of the direction of change in demand except what might be guessed by the buyers from the al- teration of their individual reserv a t ion prices When trading began (period 1 test 5B) the immediate response was a very considerable upward sweep in exchange prices with several contracts being closed in the first trading period well above the new higher ecluilibrium price Indeed the eagerness to buy was so strong that two sellers who were submar- ginal both before and after the increase in demand (their reservation prices were

W o t e also that there was a small (one-unit) decrease in supply from SS to SS This was not planned It was due to the inal~ility of one sul~ject (the seller with the $210 reservation price) in test 5A to participate in test 5B Therefore except for the deletion of this one seller from the market the conditions of supply r e r e not altered that is the scllc~s ol test 5 B retni~~cclthe same rcscrvation 1)ricc cards as they liad ill test 51

$350 and $370) were able to m~bc con- tracts in this transient phase of the mar- ket Consecluently the trading group showing the strongest equilibrating ten- dencies exhibited very erratic behavior in the transient phase following the in- crease in demand Contract prices greatly overshot the new equilibrium and ration- ing by the market was less efficient in this transient phase In the second tratl- ing period of test 5B no submarginal sellers or buyers made contracts and tllc inarket exhibited a narrowed movcment toward the new equilibrium

Test 611 was designed to determine whether market equilibrium was affected by a marlred imbalance between the number of intramarginal sellers and the number of intramarginal buyers near the predicted equilibrium price The demand curve DD in Chart 6 falls continuously to the right in one-unit steps while the supply curve SS becomes perfectly in- elastic a t the price $400 well below the equilibrium price $1075 The tenta- tive hypothesis was that the large rent ($675) enjoyed by the marginal seller with still larger rents for the intramar- ginal sellers might prevent the theoreti- cal equilibrium from being established From the results it is seen that the earlier conjecture concerning the efiect of a divergence between buyer and seller rent on the approach to equilibrium is confirmed The approach to ecluilibrium is from below and the convergence is relatively slow However there is no indication that the lack of marginal sell- ers near the theoretical equilibrium has prevented the equilibrium from being attained The average contract price in trading period 4 is $1090 only $015 above the predicted equilibrium

4t the close of trading period 4 in test 611 thc old buyer cards correspond- ing to DD were rcplaced by new cards

correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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114 -ERNOX I SlITTII

of a trading period this procedure is continued until bids and ofters are no longer leading to contracts One or two calls are made for final bids or offers and the market is officially closed This ends period 1 The market is then im- mediately reopened for the second day of trading All buyers including those who did and those who did not make coiltracts in the preceding trading period i ~ o x ~ ~(as explained previously to the sub- jects) have a renewed urge to buy one unit of the commodity For each buyer the same maximum buying price holds in the second period as prevailed in the first period In this way the experimental demand curve represents a demand per unit time or per trading period Similarly each seller we may imagine has over- night acquired a fresh unit of the com- modity which he desires to sell in period 2 under the same minimum price con-ditions as prevailed in period 1 The experimental supply curve thereby repre- sents a willingness to supply per unit time Trading period 2 is allowed to run its course arlcl then period 3 and so on By this means we construct a prototype market in which there is a flow of a commodity onto and off the market The stage is thereby set to study price behavior under given conditions of nor- mal supply and demand5 Some buyers and sellers it should be noted may be unable to make contracts in any trading period or perhaps only in certain peri- ods Tnsofar as these traders are sub-marginal buyers or sellers this is to be eupected Indeed the ability of these experimental markets to ration out sub- marginal buyers and sellers will be one measure of the effectiveness or competi- tive performance of the market

The above design considerations define a rejection set of offers (and bids) for each I~uyer (and seller) which in turn

defines a demand and a supply schedule for the marliet in question-These sched- ules do nothing beyond setting extreme limits to the observable price-quantity behavior in that marliet All we can say is that the area above the supply curve is a region in which sales are feasible while tvhe area below the demand curve is a region in which purchases are feasi- ble ~ ~ m ~ e t i t i v e price theory asserts that there will be a tendency for price-quan- tity equilibrium to occur a t the extreme quantity point of the intersection of these G o areas For example in Chart 1 the shaded triangular area APB represents the intersection of these feasible sales and purchase sets with P the extreme point of this set We have no guarantee that the equilibrium defined by the inter- section of these sets will prevail even approximately in the experimental mar- ket (or any real counterpart of it) The mere fact that by any definition supply and demand schedules exist in the back- ground of a market does not guarantee that any meaningful relationship exists

The design of my experiments differs from that of Chamberlin (op cit) in several ways I n Chamber- lms experinlent the buyers and sellers simply cir- culate and engage in bilateral higgling and bargaining until they make a contract or the trading perioti ends As contracts are made the transaction price is recorded on the blackboard Consecluently there is very little if any multilateral bidding Each traders attention is directed to the one person with whom he is bargaining nhereas in my experiments each traders quotation is addressed to the entire trading group one quotation a t a time Also Cham- berlins experiment constitutes a pure exchange mar- ket operated for a single trading period There is therefore less opportunity for traders to gain experience and to modify their subsequent behavior in the light of such experience I t is only through some learning mechanism of this kind that I can imagine the possibility of equilibrium being ap-proached in any real market Finally in the present experiments I have varied the design from one experiment to another in a conscious attempt to study the effect of different conditions of supply and demand changes in supply or demand and changes in the rules of market organization on market-price behavior

ESPERIRlTSTL STTI)Y OF COLIPETITIIlt RI 4RKET BEH ITOR 115

between those schedules and what is ob- served in the market they are presumed to represent =11 the supply and demand schedules can do is set broad limits on the behavior of the market6 Thus in the symmetrical supply and demand dia- gram of Chart 3 it is conceivable that every buyer ant1 seller could make a contract The $325 buyer could buy from the $325 seller the $300 buyer could buy from the $300 seller and so forth wiihout violating any restrictions on the behavior of buyers and sellers Tntleed if we separately paired buyers and sellers in this special way each pair could be expectetl to make a bilateral contract a t the sellers miilimum price which ~voulti be equal to the buyers maximum price

I t should be noted that these e s ~ e r i - ments conform in several important ways to what we know must be true of many kinds of real markets In a real competi- tive market such as a commodity or stock exchange each marketer is likely to be ignorant of the reservation prices a t which other buyers and sellers are willing to trade Furthermore the only m y that a real marketer can obtain 1tiowletlge of market conditions is to

V n fact these schetlues are motiiiled as trading takes place Vhenevci- a ljuyer and a seller make a contract and drol) out of the market the demancl and supl)ly schetlules are shifted to the left in a nianner tlepentli~lg upon tlie buyers atid sellers position on the schetlules Iience the supply and tiemand ru~ictions co~itinually alter as the trading process occul-s I t is ~IiLhc~~it to imagine a real market ~xoccss which does not exhibit this characteristic Ihis means that the intra-trading-~~eriotl schedules are not iridepentlent of the transac~ions taking place FIo-ever the iiziiial schedules prevailirig a t the openilig of each trading period are independent of the transactions and it is these schedules that I identify with the theoretical conditions of supply and tlcmand which the theorist delines independ- ently of actual niarket prices and quantities One ol the importallt ol~jrctives in these experiments is to determine whether or not these irlitial schetlules have any power to ~)retlict the observetl behavior ol the market

observe the offers and bids that are ten- dered and whether or not they are ac- cepted These are the public data of the market A marketer can only know his own attitude and from observation learn something about the objective be- havior of others This is a major feature of these experimental markets We de- liberately avoid placing a t the disposal of our subjects any information which would not be practically attainable in a real market Each experimental market is forced to provide all of its own his- tory These markets are also a replica of real markets in that they are com-posed of a practical number of market- ers say twenty thirty or forty We do not require an indefinitely large number of marketers ~v l~ ich is usually supposed necessary for the existence of pure competition

One important condition operating in our experimental markets is not likely to prevail in real markets The experi- mental conditions of supply and demand are held constant over several successive trading periods in order to give any equilibrating mechanisms an opportuni- ty to establish an equilibrium over time Real markets are likely to be continu- ally subjected to changing conditions of supply and demand hlarshall was well aware of such problems and defined equi- librium as a condition toward which the market would move if the forces of sup- ply and demand were to remain station- ary for a sufficiently long time I t is this concept of equilibrium that this par- ticular series of experiments is designed in part to test There is nothing to prevent one from passing out new buyer andor seller cards representing changed demand andor supply conditions a t the end of each trading period if the objective is to study the effect of such constantly changing conditions on market behavior

In three of the nine experiments once- for-all changes in demand andor supply were made for purposes of studying the transient dynamics of a markets re-sponse to such stimuli

111 DESCRIPTION A h D DISCUSSION

OF E X P E R I M E N T A L RESULTS

The supply and demand schedule for each experiment is shown in the diagram on the left of Charts 1-10 The price and quantity a t which these schedules intersect will be referred to as the pre- dicted or theoretical equilibrium price and quantity for the corresponding ex- perimental market though such an equilibrium will not necessarily be attained or approached in the market The performance of each experimental market is summarized in the diagram on the right of Charts 1-10 and in Table 1 Each chart shows the sequence of contract or exchange prices in the order in which they occurred in each trading period Thus in Chart 1 the first transaction was effected a t $170 the second a t $180 and so on with a total of five transactions occurring in trading period 1 These charts show con- tract price as a function of transaction number rather than calendar time the latter of course being quite irrelevant to market dynamics

The most striking general characteris- tic of tests 1-3 5-7 9 and 10 is the remarkably strong tendency for exchange prices to approach the predicted equi- librium for each of these markets As the exchange process is repeated through successive trading periods with the same conditions of supply and demand pre- vailing initially in each period the varia- tion in exchange prices tends to decline and to cluster more closely around the equilibrium In Chart 1 for esample the variation in contract prices over the five

trading periods is from $170 to $225 The maximum possible variation is from $075 to $325 as seen in the supply and demand schedules As a means of measuring the convergence of exchange prices in each market a coefficient of convergence a has been coi~~puted for each trading period in each market The a for each trading period is the ratio of the standard deviation of exchange prices a to the predicted equilibriun~ price Po the ratio being expressed as a percentage That is a = 100 aolPo where a is the standard deviation of exchange prices around the equilibrium price rather than the mean exchange price Hence a provides a 111easure of exchange price variation relative to the predicted equilibrium exchange price is is seen in Table 1 and the charts for all tests except test 8 a tends to decline from one trading period to the next with tests 2 4A 5 6A 7 9A and 10 showing monotone convergence

Turning now to the individual experi- mental results it will be observed that the equilibrium price and quantity are approxin~ately the same for the supply and demand curves of tests 2 and 3 The significant difference in the design of these two tests is that the supply and demand schedules for test 2 are relatively flat while the corresponding schedules for test 3 are much more steep- ly inclined

Under the Walrasian hypothesis (the rate of increase in exchange price is an increasing function of the excess demand a t that price) one would expect the market in test 2 to converge more rapidly than that in test 3 As is evident from comparing the results in Charts 2 and 3 test 2 shows a more rapid and less er- ratic tendency toward equilibrium These results are of course cnnristent with many otller hypotheses including the

Irc- Coef- Ao of Sub Xo of SUE I clicted r~Luill ficient marginalAverage No of Sub- marginal s o of Sub-

Ex- Ex- of Con- H u q e ~ sActual marginal Sellers marginal clrdngc chaigc vergence n h oI ~ ~ ~ l ~ a n g c lloyers ho Sellers Qunn-

t i t y (30)

Quan-t i ty (XI

[a=

(100 un) (Po)I

Could AIaBc

Contractb

Price (r)

Who lade Coritracts

Could M a k e

Con t racts

Viio hladc Colltracts

---- -1-

1 6 5 5 6 3 5 6 5 5 6 7 5 6 6 5

15 16 4 15 15 4 15 16 4

16 17 5 16 5 16 5 16 3

10 None xone None Kone 10 None h-one xone None 10 None None Kone hTone 10 None Kone None None

8 None None None 8 None None None 8 None None None

10 10 10 10

12 12

12 None 12 Kone 12 hone 12 None

None None None None None None None hone Kone hone hTone None

xone None None None xone None

352 103 3 3 2

317 110 4 2 None None 336 3 2 4 1 None Kone 338 2 2 4 0 None None

CHART 2

0 2 4 6 8 10 12 14 16 18 20 2 2 1 4 8 12 17 4 8 12 15 4 O I 15 1 8 i 19

QUANTITY TRAN6ACTiC)N I 4 l i l G F i l I b Y P Rlgtl

excess-rent hypothesis to be discussed later7

The tests in Chart 4 are of special interest from the point of view of the Walrasian hypothesis In this case the supply curve is perfectly elastic-all sell-ers have cards containing the price $310 Each seller has the same lower bound on his reservation price acceptance set

equilibrium since there is a considerable excess supply a t prices just barely above the equilibrium price From the results we see that the market is not particularly slow in converging but i t converges to a fairly stable price about $020 above the predicted equilibrium Furthermore in test 4B which was an extension of 4A the interjection of a decrease in

CHART 4

TEST 4 A AND TEST 48 I6 C O I

- -- --- -580 -560 -5 4 0 - s

520 -

-5 00

Po 1310 Xo10

4 6 0 -

4 2 0 -u

2- 4 3 0 -+DECREASE

3 s o -

3 6 3 -

3 4 0

3 20

300

2 8 0

2 2 0 I

$ 6 0 0

5 80

560

5 4 0

5 2 0

5 0 0

4 80

460

4 4 0

4 20

IN DEMAYD+- O0

3 80

360

3 4 0

3 2 0

- 280

200 1 2 3 4 5 6 7 8 9 10 11 12 1 3 3 5 7 V I 3 5 7 V 1 3 5 7 9 1 3 5 7 9 1 3 5 7 8 1 3 5 7 1 3 5 6

Q ~ I A U T I T Y

In thi5 senie 11erc is no tlivergencc of attitude among the sellers though there might be marked variation in their bar- gaining propensities According to the Walrasian hypothesis this market should exhibit rapid convergence toward the

I T h e results are inconsistent n i t h the so-called hfarshallian hypothesis (the rate of increase in quan- tit) exchanged is an increasing function of the excess of demand price over supply price) but this hy- pothesis nould seem to be worth considering only in market processes in which some quantity-adjust- ing decision is made by the marketers The results of a pilot experiment in short-run and long-run equilibrium are displayed in the Appendix

TRANSACTION NUMBER ( B Y PERIOD1

demand from DD to DID was ineffective as a means of shocking the market down to its supply and demand equilibrium This decrease in demand was achieved by passing out new buyer cards corre- sponding to DD a t the close of period

in test 4A As the market approaches equilibrium from above since contracts a t prices below equilibrium are

The sellers in this market presented 3 solid front against price being lowered to ecluilibrium In the previous mar-

120 VERNON L SYIITFT

kets there was a divergence of seller attitude so that only a very few mar- ginal and near-marginal sellers might offer serious resistance to price being forced to equilibrium And this resistance tended to break down when any of the stronger intramarginal sellers accepted contracts below equilibrium

From these results it is clear that the static competitive market equilibri- um may depend not only on the inter- section of the supply and demanci sched- ules but also upon the shapes of the schedules Specifically I was led from test 4 to the tentative hypothesis that there may be an upward bias in the equilibrium price of a market which will be greater the more elastic is the supply schedule relative to demand8 For example let A be the area under the demand schedule and above the theoreti- cal equilibrium This is Alarshalls con-sumer surplus but to avoid any welfare connotations of this term I shall refer to the area as buyers rent Let B be the area above the supply schedule and below the theoretical equilibrium (Marshalls producer surplus) which I shall call sellers rent Now the tenta- tive hypothesis was that the actual mar- ket ecjuilibrium will be above the the- oretical equilibrium by an amount which depends upon how large A is relative to B Similarly there will be a downward bias if A is small relative to B

Test 4 is of course an extreme case since B = 0 In test 3 A is larger than B and the trading periods 3 and 4 ex-hibit a slight upward bias in the average actual exchange price (see Table 1) This provides some slight evidence in favor of the hypothesis

8 Note that the LValrasian hypothesis might lead one to expect a dol~nward bias since excess supply is very large at prices above equilihriuni if sup1)ly is very elastic relative to demand

As a consequence of these considera- tions test 7 was designed specifically to obtain additional information to sup- port or contradict the indicated hypothe- sis In this case as is seen in Chart 7 (see below) buyers rent is substan- tially smaller than sellers rent From the resulting course of contract prices over six trading periods in this experi- ment it is evident that the convergence to equilibrium is very slow From Table 1 the average exchange prices in the last three trading periods are respec- tively $332 $333 and $334 Average contract prices are still exhibiting a grad- ual approach to equilibrium Hence i t is entirely possible that the static equi- librium would eventually have been at- tained A still smaller buyers rent may be required to provide any clear down- ward bias in the static equilibrium One thing however seems quite unmistak- able from Chart 7 the relative magni- tude of buyers and sellers rent affects the speed with which the actual market equilibrium is approached One would expect sellers to present a somewhat weaker bargaining front especially a t first if their rent potential is large rela- tive to that of buyers Thus in Chart 7 i t is seen that several low reservation price sellers in trading periocls 1 and 2 made contracts a t low exchange prices which no doubt seemed quite profit- able to these sellers However in both these trading periods the later exchange prices were much higher revealing to the lour-price sellers that however prof- itable their initial sales had been still greater proLts were possible under stiffer bargaining

-4 stronger test of the hypotheses that buyer and seller rents affect the speed of adjustment and that they affect the final equil1rillln in the market would t)e ohtainal~lc l)j-introclucing actual mon-

etary payoffs in the experiment Thus one might offer to pay each seller the difference between his contract price and his reservation price and each buyer the difference between his reservation price and his contract price In addition one might pay each trader a small lump sum (say $005) just for making a contract in any period This sum would represent

GJeYTITi

iinormal pro~its that is a small return even if the good is sold a t its minimum supply price or purchased a t its maxi- mum demand price The present experi- ments have not seemeti to provide any motivation problems The subjects have shown high motivation to do their best even without monetary payo-tis But our experimental marginal buyers and sellers may be more reluctant to approach their reservation prices than their counter-parts in real markets The use oi nlone-tary payoifs as suggested should remox c

any such reluctance that is attributable to artificial elements in the present cx-peri i~lents ~

The experinlent summarized in Chart 5 was designed to study the effect on market behavior of changes in the condi- tions of demand and supply As it hap- pened this ex1)eriment was performed on a considerably more mature group

T R A N S A C T O N NJMBER ( 3 1 Pi11331

of subjects than any of the other experi- rnents Alost of the experiments were performed on sophornore ant1 junior en-gineering economics and business ma-jors while test 5 was performed on a

Since this was witten an experiment has been tried using monetary payofis and the same supply and demand design shown in Chart 4 The result as conjectured in the text TYas to remove the reluc- tance of sellers to sell at their reservation prices Ey the second trading period the market vas firmly in equilibrium In the thirtl period all trades were at $3ti) Al)parcntly$005 per pcriocl as considerecl satisfactory normal prolit

graduate class in econoinic theory 111

view of this dilference it is most interest- ing to find the phenomenally low values for a exhibited by test 5A The coefficient of convergence is smaller for the opening and later periods of this inarket than for any period of any of the other tests Furthermore trading periods 2-4 show as of less than 1 per cent indicating an inordinately strong and rapid tenden- cy toward equilibrium In this case no offers or bids were accepted until the bidding had converged to prices which were very near indeed to the ecluilibrium Contract prices ranged from $300 to S320 as compared with a possible range from $210 to $375

-It the close of test 5A new cards were distributed correspontling to an increase in demand from DD to DID as shown in Chart 51deg The subjects of course could guess from the fact that new buy- er cards were being distributed that a change in demand was in the wind But they knew nothing of the direction of change in demand except what might be guessed by the buyers from the al- teration of their individual reserv a t ion prices When trading began (period 1 test 5B) the immediate response was a very considerable upward sweep in exchange prices with several contracts being closed in the first trading period well above the new higher ecluilibrium price Indeed the eagerness to buy was so strong that two sellers who were submar- ginal both before and after the increase in demand (their reservation prices were

W o t e also that there was a small (one-unit) decrease in supply from SS to SS This was not planned It was due to the inal~ility of one sul~ject (the seller with the $210 reservation price) in test 5A to participate in test 5B Therefore except for the deletion of this one seller from the market the conditions of supply r e r e not altered that is the scllc~s ol test 5 B retni~~cclthe same rcscrvation 1)ricc cards as they liad ill test 51

$350 and $370) were able to m~bc con- tracts in this transient phase of the mar- ket Consecluently the trading group showing the strongest equilibrating ten- dencies exhibited very erratic behavior in the transient phase following the in- crease in demand Contract prices greatly overshot the new equilibrium and ration- ing by the market was less efficient in this transient phase In the second tratl- ing period of test 5B no submarginal sellers or buyers made contracts and tllc inarket exhibited a narrowed movcment toward the new equilibrium

Test 611 was designed to determine whether market equilibrium was affected by a marlred imbalance between the number of intramarginal sellers and the number of intramarginal buyers near the predicted equilibrium price The demand curve DD in Chart 6 falls continuously to the right in one-unit steps while the supply curve SS becomes perfectly in- elastic a t the price $400 well below the equilibrium price $1075 The tenta- tive hypothesis was that the large rent ($675) enjoyed by the marginal seller with still larger rents for the intramar- ginal sellers might prevent the theoreti- cal equilibrium from being established From the results it is seen that the earlier conjecture concerning the efiect of a divergence between buyer and seller rent on the approach to equilibrium is confirmed The approach to ecluilibrium is from below and the convergence is relatively slow However there is no indication that the lack of marginal sell- ers near the theoretical equilibrium has prevented the equilibrium from being attained The average contract price in trading period 4 is $1090 only $015 above the predicted equilibrium

4t the close of trading period 4 in test 611 thc old buyer cards correspond- ing to DD were rcplaced by new cards

correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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ESPERIRlTSTL STTI)Y OF COLIPETITIIlt RI 4RKET BEH ITOR 115

between those schedules and what is ob- served in the market they are presumed to represent =11 the supply and demand schedules can do is set broad limits on the behavior of the market6 Thus in the symmetrical supply and demand dia- gram of Chart 3 it is conceivable that every buyer ant1 seller could make a contract The $325 buyer could buy from the $325 seller the $300 buyer could buy from the $300 seller and so forth wiihout violating any restrictions on the behavior of buyers and sellers Tntleed if we separately paired buyers and sellers in this special way each pair could be expectetl to make a bilateral contract a t the sellers miilimum price which ~voulti be equal to the buyers maximum price

I t should be noted that these e s ~ e r i - ments conform in several important ways to what we know must be true of many kinds of real markets In a real competi- tive market such as a commodity or stock exchange each marketer is likely to be ignorant of the reservation prices a t which other buyers and sellers are willing to trade Furthermore the only m y that a real marketer can obtain 1tiowletlge of market conditions is to

V n fact these schetlues are motiiiled as trading takes place Vhenevci- a ljuyer and a seller make a contract and drol) out of the market the demancl and supl)ly schetlules are shifted to the left in a nianner tlepentli~lg upon tlie buyers atid sellers position on the schetlules Iience the supply and tiemand ru~ictions co~itinually alter as the trading process occul-s I t is ~IiLhc~~it to imagine a real market ~xoccss which does not exhibit this characteristic Ihis means that the intra-trading-~~eriotl schedules are not iridepentlent of the transac~ions taking place FIo-ever the iiziiial schedules prevailirig a t the openilig of each trading period are independent of the transactions and it is these schedules that I identify with the theoretical conditions of supply and tlcmand which the theorist delines independ- ently of actual niarket prices and quantities One ol the importallt ol~jrctives in these experiments is to determine whether or not these irlitial schetlules have any power to ~)retlict the observetl behavior ol the market

observe the offers and bids that are ten- dered and whether or not they are ac- cepted These are the public data of the market A marketer can only know his own attitude and from observation learn something about the objective be- havior of others This is a major feature of these experimental markets We de- liberately avoid placing a t the disposal of our subjects any information which would not be practically attainable in a real market Each experimental market is forced to provide all of its own his- tory These markets are also a replica of real markets in that they are com-posed of a practical number of market- ers say twenty thirty or forty We do not require an indefinitely large number of marketers ~v l~ ich is usually supposed necessary for the existence of pure competition

One important condition operating in our experimental markets is not likely to prevail in real markets The experi- mental conditions of supply and demand are held constant over several successive trading periods in order to give any equilibrating mechanisms an opportuni- ty to establish an equilibrium over time Real markets are likely to be continu- ally subjected to changing conditions of supply and demand hlarshall was well aware of such problems and defined equi- librium as a condition toward which the market would move if the forces of sup- ply and demand were to remain station- ary for a sufficiently long time I t is this concept of equilibrium that this par- ticular series of experiments is designed in part to test There is nothing to prevent one from passing out new buyer andor seller cards representing changed demand andor supply conditions a t the end of each trading period if the objective is to study the effect of such constantly changing conditions on market behavior

In three of the nine experiments once- for-all changes in demand andor supply were made for purposes of studying the transient dynamics of a markets re-sponse to such stimuli

111 DESCRIPTION A h D DISCUSSION

OF E X P E R I M E N T A L RESULTS

The supply and demand schedule for each experiment is shown in the diagram on the left of Charts 1-10 The price and quantity a t which these schedules intersect will be referred to as the pre- dicted or theoretical equilibrium price and quantity for the corresponding ex- perimental market though such an equilibrium will not necessarily be attained or approached in the market The performance of each experimental market is summarized in the diagram on the right of Charts 1-10 and in Table 1 Each chart shows the sequence of contract or exchange prices in the order in which they occurred in each trading period Thus in Chart 1 the first transaction was effected a t $170 the second a t $180 and so on with a total of five transactions occurring in trading period 1 These charts show con- tract price as a function of transaction number rather than calendar time the latter of course being quite irrelevant to market dynamics

The most striking general characteris- tic of tests 1-3 5-7 9 and 10 is the remarkably strong tendency for exchange prices to approach the predicted equi- librium for each of these markets As the exchange process is repeated through successive trading periods with the same conditions of supply and demand pre- vailing initially in each period the varia- tion in exchange prices tends to decline and to cluster more closely around the equilibrium In Chart 1 for esample the variation in contract prices over the five

trading periods is from $170 to $225 The maximum possible variation is from $075 to $325 as seen in the supply and demand schedules As a means of measuring the convergence of exchange prices in each market a coefficient of convergence a has been coi~~puted for each trading period in each market The a for each trading period is the ratio of the standard deviation of exchange prices a to the predicted equilibriun~ price Po the ratio being expressed as a percentage That is a = 100 aolPo where a is the standard deviation of exchange prices around the equilibrium price rather than the mean exchange price Hence a provides a 111easure of exchange price variation relative to the predicted equilibrium exchange price is is seen in Table 1 and the charts for all tests except test 8 a tends to decline from one trading period to the next with tests 2 4A 5 6A 7 9A and 10 showing monotone convergence

Turning now to the individual experi- mental results it will be observed that the equilibrium price and quantity are approxin~ately the same for the supply and demand curves of tests 2 and 3 The significant difference in the design of these two tests is that the supply and demand schedules for test 2 are relatively flat while the corresponding schedules for test 3 are much more steep- ly inclined

Under the Walrasian hypothesis (the rate of increase in exchange price is an increasing function of the excess demand a t that price) one would expect the market in test 2 to converge more rapidly than that in test 3 As is evident from comparing the results in Charts 2 and 3 test 2 shows a more rapid and less er- ratic tendency toward equilibrium These results are of course cnnristent with many otller hypotheses including the

Irc- Coef- Ao of Sub Xo of SUE I clicted r~Luill ficient marginalAverage No of Sub- marginal s o of Sub-

Ex- Ex- of Con- H u q e ~ sActual marginal Sellers marginal clrdngc chaigc vergence n h oI ~ ~ ~ l ~ a n g c lloyers ho Sellers Qunn-

t i t y (30)

Quan-t i ty (XI

[a=

(100 un) (Po)I

Could AIaBc

Contractb

Price (r)

Who lade Coritracts

Could M a k e

Con t racts

Viio hladc Colltracts

---- -1-

1 6 5 5 6 3 5 6 5 5 6 7 5 6 6 5

15 16 4 15 15 4 15 16 4

16 17 5 16 5 16 5 16 3

10 None xone None Kone 10 None h-one xone None 10 None None Kone hTone 10 None Kone None None

8 None None None 8 None None None 8 None None None

10 10 10 10

12 12

12 None 12 Kone 12 hone 12 None

None None None None None None None hone Kone hone hTone None

xone None None None xone None

352 103 3 3 2

317 110 4 2 None None 336 3 2 4 1 None Kone 338 2 2 4 0 None None

CHART 2

0 2 4 6 8 10 12 14 16 18 20 2 2 1 4 8 12 17 4 8 12 15 4 O I 15 1 8 i 19

QUANTITY TRAN6ACTiC)N I 4 l i l G F i l I b Y P Rlgtl

excess-rent hypothesis to be discussed later7

The tests in Chart 4 are of special interest from the point of view of the Walrasian hypothesis In this case the supply curve is perfectly elastic-all sell-ers have cards containing the price $310 Each seller has the same lower bound on his reservation price acceptance set

equilibrium since there is a considerable excess supply a t prices just barely above the equilibrium price From the results we see that the market is not particularly slow in converging but i t converges to a fairly stable price about $020 above the predicted equilibrium Furthermore in test 4B which was an extension of 4A the interjection of a decrease in

CHART 4

TEST 4 A AND TEST 48 I6 C O I

- -- --- -580 -560 -5 4 0 - s

520 -

-5 00

Po 1310 Xo10

4 6 0 -

4 2 0 -u

2- 4 3 0 -+DECREASE

3 s o -

3 6 3 -

3 4 0

3 20

300

2 8 0

2 2 0 I

$ 6 0 0

5 80

560

5 4 0

5 2 0

5 0 0

4 80

460

4 4 0

4 20

IN DEMAYD+- O0

3 80

360

3 4 0

3 2 0

- 280

200 1 2 3 4 5 6 7 8 9 10 11 12 1 3 3 5 7 V I 3 5 7 V 1 3 5 7 9 1 3 5 7 9 1 3 5 7 8 1 3 5 7 1 3 5 6

Q ~ I A U T I T Y

In thi5 senie 11erc is no tlivergencc of attitude among the sellers though there might be marked variation in their bar- gaining propensities According to the Walrasian hypothesis this market should exhibit rapid convergence toward the

I T h e results are inconsistent n i t h the so-called hfarshallian hypothesis (the rate of increase in quan- tit) exchanged is an increasing function of the excess of demand price over supply price) but this hy- pothesis nould seem to be worth considering only in market processes in which some quantity-adjust- ing decision is made by the marketers The results of a pilot experiment in short-run and long-run equilibrium are displayed in the Appendix

TRANSACTION NUMBER ( B Y PERIOD1

demand from DD to DID was ineffective as a means of shocking the market down to its supply and demand equilibrium This decrease in demand was achieved by passing out new buyer cards corre- sponding to DD a t the close of period

in test 4A As the market approaches equilibrium from above since contracts a t prices below equilibrium are

The sellers in this market presented 3 solid front against price being lowered to ecluilibrium In the previous mar-

120 VERNON L SYIITFT

kets there was a divergence of seller attitude so that only a very few mar- ginal and near-marginal sellers might offer serious resistance to price being forced to equilibrium And this resistance tended to break down when any of the stronger intramarginal sellers accepted contracts below equilibrium

From these results it is clear that the static competitive market equilibri- um may depend not only on the inter- section of the supply and demanci sched- ules but also upon the shapes of the schedules Specifically I was led from test 4 to the tentative hypothesis that there may be an upward bias in the equilibrium price of a market which will be greater the more elastic is the supply schedule relative to demand8 For example let A be the area under the demand schedule and above the theoreti- cal equilibrium This is Alarshalls con-sumer surplus but to avoid any welfare connotations of this term I shall refer to the area as buyers rent Let B be the area above the supply schedule and below the theoretical equilibrium (Marshalls producer surplus) which I shall call sellers rent Now the tenta- tive hypothesis was that the actual mar- ket ecjuilibrium will be above the the- oretical equilibrium by an amount which depends upon how large A is relative to B Similarly there will be a downward bias if A is small relative to B

Test 4 is of course an extreme case since B = 0 In test 3 A is larger than B and the trading periods 3 and 4 ex-hibit a slight upward bias in the average actual exchange price (see Table 1) This provides some slight evidence in favor of the hypothesis

8 Note that the LValrasian hypothesis might lead one to expect a dol~nward bias since excess supply is very large at prices above equilihriuni if sup1)ly is very elastic relative to demand

As a consequence of these considera- tions test 7 was designed specifically to obtain additional information to sup- port or contradict the indicated hypothe- sis In this case as is seen in Chart 7 (see below) buyers rent is substan- tially smaller than sellers rent From the resulting course of contract prices over six trading periods in this experi- ment it is evident that the convergence to equilibrium is very slow From Table 1 the average exchange prices in the last three trading periods are respec- tively $332 $333 and $334 Average contract prices are still exhibiting a grad- ual approach to equilibrium Hence i t is entirely possible that the static equi- librium would eventually have been at- tained A still smaller buyers rent may be required to provide any clear down- ward bias in the static equilibrium One thing however seems quite unmistak- able from Chart 7 the relative magni- tude of buyers and sellers rent affects the speed with which the actual market equilibrium is approached One would expect sellers to present a somewhat weaker bargaining front especially a t first if their rent potential is large rela- tive to that of buyers Thus in Chart 7 i t is seen that several low reservation price sellers in trading periocls 1 and 2 made contracts a t low exchange prices which no doubt seemed quite profit- able to these sellers However in both these trading periods the later exchange prices were much higher revealing to the lour-price sellers that however prof- itable their initial sales had been still greater proLts were possible under stiffer bargaining

-4 stronger test of the hypotheses that buyer and seller rents affect the speed of adjustment and that they affect the final equil1rillln in the market would t)e ohtainal~lc l)j-introclucing actual mon-

etary payoffs in the experiment Thus one might offer to pay each seller the difference between his contract price and his reservation price and each buyer the difference between his reservation price and his contract price In addition one might pay each trader a small lump sum (say $005) just for making a contract in any period This sum would represent

GJeYTITi

iinormal pro~its that is a small return even if the good is sold a t its minimum supply price or purchased a t its maxi- mum demand price The present experi- ments have not seemeti to provide any motivation problems The subjects have shown high motivation to do their best even without monetary payo-tis But our experimental marginal buyers and sellers may be more reluctant to approach their reservation prices than their counter-parts in real markets The use oi nlone-tary payoifs as suggested should remox c

any such reluctance that is attributable to artificial elements in the present cx-peri i~lents ~

The experinlent summarized in Chart 5 was designed to study the effect on market behavior of changes in the condi- tions of demand and supply As it hap- pened this ex1)eriment was performed on a considerably more mature group

T R A N S A C T O N NJMBER ( 3 1 Pi11331

of subjects than any of the other experi- rnents Alost of the experiments were performed on sophornore ant1 junior en-gineering economics and business ma-jors while test 5 was performed on a

Since this was witten an experiment has been tried using monetary payofis and the same supply and demand design shown in Chart 4 The result as conjectured in the text TYas to remove the reluc- tance of sellers to sell at their reservation prices Ey the second trading period the market vas firmly in equilibrium In the thirtl period all trades were at $3ti) Al)parcntly$005 per pcriocl as considerecl satisfactory normal prolit

graduate class in econoinic theory 111

view of this dilference it is most interest- ing to find the phenomenally low values for a exhibited by test 5A The coefficient of convergence is smaller for the opening and later periods of this inarket than for any period of any of the other tests Furthermore trading periods 2-4 show as of less than 1 per cent indicating an inordinately strong and rapid tenden- cy toward equilibrium In this case no offers or bids were accepted until the bidding had converged to prices which were very near indeed to the ecluilibrium Contract prices ranged from $300 to S320 as compared with a possible range from $210 to $375

-It the close of test 5A new cards were distributed correspontling to an increase in demand from DD to DID as shown in Chart 51deg The subjects of course could guess from the fact that new buy- er cards were being distributed that a change in demand was in the wind But they knew nothing of the direction of change in demand except what might be guessed by the buyers from the al- teration of their individual reserv a t ion prices When trading began (period 1 test 5B) the immediate response was a very considerable upward sweep in exchange prices with several contracts being closed in the first trading period well above the new higher ecluilibrium price Indeed the eagerness to buy was so strong that two sellers who were submar- ginal both before and after the increase in demand (their reservation prices were

W o t e also that there was a small (one-unit) decrease in supply from SS to SS This was not planned It was due to the inal~ility of one sul~ject (the seller with the $210 reservation price) in test 5A to participate in test 5B Therefore except for the deletion of this one seller from the market the conditions of supply r e r e not altered that is the scllc~s ol test 5 B retni~~cclthe same rcscrvation 1)ricc cards as they liad ill test 51

$350 and $370) were able to m~bc con- tracts in this transient phase of the mar- ket Consecluently the trading group showing the strongest equilibrating ten- dencies exhibited very erratic behavior in the transient phase following the in- crease in demand Contract prices greatly overshot the new equilibrium and ration- ing by the market was less efficient in this transient phase In the second tratl- ing period of test 5B no submarginal sellers or buyers made contracts and tllc inarket exhibited a narrowed movcment toward the new equilibrium

Test 611 was designed to determine whether market equilibrium was affected by a marlred imbalance between the number of intramarginal sellers and the number of intramarginal buyers near the predicted equilibrium price The demand curve DD in Chart 6 falls continuously to the right in one-unit steps while the supply curve SS becomes perfectly in- elastic a t the price $400 well below the equilibrium price $1075 The tenta- tive hypothesis was that the large rent ($675) enjoyed by the marginal seller with still larger rents for the intramar- ginal sellers might prevent the theoreti- cal equilibrium from being established From the results it is seen that the earlier conjecture concerning the efiect of a divergence between buyer and seller rent on the approach to equilibrium is confirmed The approach to ecluilibrium is from below and the convergence is relatively slow However there is no indication that the lack of marginal sell- ers near the theoretical equilibrium has prevented the equilibrium from being attained The average contract price in trading period 4 is $1090 only $015 above the predicted equilibrium

4t the close of trading period 4 in test 611 thc old buyer cards correspond- ing to DD were rcplaced by new cards

correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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In three of the nine experiments once- for-all changes in demand andor supply were made for purposes of studying the transient dynamics of a markets re-sponse to such stimuli

111 DESCRIPTION A h D DISCUSSION

OF E X P E R I M E N T A L RESULTS

The supply and demand schedule for each experiment is shown in the diagram on the left of Charts 1-10 The price and quantity a t which these schedules intersect will be referred to as the pre- dicted or theoretical equilibrium price and quantity for the corresponding ex- perimental market though such an equilibrium will not necessarily be attained or approached in the market The performance of each experimental market is summarized in the diagram on the right of Charts 1-10 and in Table 1 Each chart shows the sequence of contract or exchange prices in the order in which they occurred in each trading period Thus in Chart 1 the first transaction was effected a t $170 the second a t $180 and so on with a total of five transactions occurring in trading period 1 These charts show con- tract price as a function of transaction number rather than calendar time the latter of course being quite irrelevant to market dynamics

The most striking general characteris- tic of tests 1-3 5-7 9 and 10 is the remarkably strong tendency for exchange prices to approach the predicted equi- librium for each of these markets As the exchange process is repeated through successive trading periods with the same conditions of supply and demand pre- vailing initially in each period the varia- tion in exchange prices tends to decline and to cluster more closely around the equilibrium In Chart 1 for esample the variation in contract prices over the five

trading periods is from $170 to $225 The maximum possible variation is from $075 to $325 as seen in the supply and demand schedules As a means of measuring the convergence of exchange prices in each market a coefficient of convergence a has been coi~~puted for each trading period in each market The a for each trading period is the ratio of the standard deviation of exchange prices a to the predicted equilibriun~ price Po the ratio being expressed as a percentage That is a = 100 aolPo where a is the standard deviation of exchange prices around the equilibrium price rather than the mean exchange price Hence a provides a 111easure of exchange price variation relative to the predicted equilibrium exchange price is is seen in Table 1 and the charts for all tests except test 8 a tends to decline from one trading period to the next with tests 2 4A 5 6A 7 9A and 10 showing monotone convergence

Turning now to the individual experi- mental results it will be observed that the equilibrium price and quantity are approxin~ately the same for the supply and demand curves of tests 2 and 3 The significant difference in the design of these two tests is that the supply and demand schedules for test 2 are relatively flat while the corresponding schedules for test 3 are much more steep- ly inclined

Under the Walrasian hypothesis (the rate of increase in exchange price is an increasing function of the excess demand a t that price) one would expect the market in test 2 to converge more rapidly than that in test 3 As is evident from comparing the results in Charts 2 and 3 test 2 shows a more rapid and less er- ratic tendency toward equilibrium These results are of course cnnristent with many otller hypotheses including the

Irc- Coef- Ao of Sub Xo of SUE I clicted r~Luill ficient marginalAverage No of Sub- marginal s o of Sub-

Ex- Ex- of Con- H u q e ~ sActual marginal Sellers marginal clrdngc chaigc vergence n h oI ~ ~ ~ l ~ a n g c lloyers ho Sellers Qunn-

t i t y (30)

Quan-t i ty (XI

[a=

(100 un) (Po)I

Could AIaBc

Contractb

Price (r)

Who lade Coritracts

Could M a k e

Con t racts

Viio hladc Colltracts

---- -1-

1 6 5 5 6 3 5 6 5 5 6 7 5 6 6 5

15 16 4 15 15 4 15 16 4

16 17 5 16 5 16 5 16 3

10 None xone None Kone 10 None h-one xone None 10 None None Kone hTone 10 None Kone None None

8 None None None 8 None None None 8 None None None

10 10 10 10

12 12

12 None 12 Kone 12 hone 12 None

None None None None None None None hone Kone hone hTone None

xone None None None xone None

352 103 3 3 2

317 110 4 2 None None 336 3 2 4 1 None Kone 338 2 2 4 0 None None

CHART 2

0 2 4 6 8 10 12 14 16 18 20 2 2 1 4 8 12 17 4 8 12 15 4 O I 15 1 8 i 19

QUANTITY TRAN6ACTiC)N I 4 l i l G F i l I b Y P Rlgtl

excess-rent hypothesis to be discussed later7

The tests in Chart 4 are of special interest from the point of view of the Walrasian hypothesis In this case the supply curve is perfectly elastic-all sell-ers have cards containing the price $310 Each seller has the same lower bound on his reservation price acceptance set

equilibrium since there is a considerable excess supply a t prices just barely above the equilibrium price From the results we see that the market is not particularly slow in converging but i t converges to a fairly stable price about $020 above the predicted equilibrium Furthermore in test 4B which was an extension of 4A the interjection of a decrease in

CHART 4

TEST 4 A AND TEST 48 I6 C O I

- -- --- -580 -560 -5 4 0 - s

520 -

-5 00

Po 1310 Xo10

4 6 0 -

4 2 0 -u

2- 4 3 0 -+DECREASE

3 s o -

3 6 3 -

3 4 0

3 20

300

2 8 0

2 2 0 I

$ 6 0 0

5 80

560

5 4 0

5 2 0

5 0 0

4 80

460

4 4 0

4 20

IN DEMAYD+- O0

3 80

360

3 4 0

3 2 0

- 280

200 1 2 3 4 5 6 7 8 9 10 11 12 1 3 3 5 7 V I 3 5 7 V 1 3 5 7 9 1 3 5 7 9 1 3 5 7 8 1 3 5 7 1 3 5 6

Q ~ I A U T I T Y

In thi5 senie 11erc is no tlivergencc of attitude among the sellers though there might be marked variation in their bar- gaining propensities According to the Walrasian hypothesis this market should exhibit rapid convergence toward the

I T h e results are inconsistent n i t h the so-called hfarshallian hypothesis (the rate of increase in quan- tit) exchanged is an increasing function of the excess of demand price over supply price) but this hy- pothesis nould seem to be worth considering only in market processes in which some quantity-adjust- ing decision is made by the marketers The results of a pilot experiment in short-run and long-run equilibrium are displayed in the Appendix

TRANSACTION NUMBER ( B Y PERIOD1

demand from DD to DID was ineffective as a means of shocking the market down to its supply and demand equilibrium This decrease in demand was achieved by passing out new buyer cards corre- sponding to DD a t the close of period

in test 4A As the market approaches equilibrium from above since contracts a t prices below equilibrium are

The sellers in this market presented 3 solid front against price being lowered to ecluilibrium In the previous mar-

120 VERNON L SYIITFT

kets there was a divergence of seller attitude so that only a very few mar- ginal and near-marginal sellers might offer serious resistance to price being forced to equilibrium And this resistance tended to break down when any of the stronger intramarginal sellers accepted contracts below equilibrium

From these results it is clear that the static competitive market equilibri- um may depend not only on the inter- section of the supply and demanci sched- ules but also upon the shapes of the schedules Specifically I was led from test 4 to the tentative hypothesis that there may be an upward bias in the equilibrium price of a market which will be greater the more elastic is the supply schedule relative to demand8 For example let A be the area under the demand schedule and above the theoreti- cal equilibrium This is Alarshalls con-sumer surplus but to avoid any welfare connotations of this term I shall refer to the area as buyers rent Let B be the area above the supply schedule and below the theoretical equilibrium (Marshalls producer surplus) which I shall call sellers rent Now the tenta- tive hypothesis was that the actual mar- ket ecjuilibrium will be above the the- oretical equilibrium by an amount which depends upon how large A is relative to B Similarly there will be a downward bias if A is small relative to B

Test 4 is of course an extreme case since B = 0 In test 3 A is larger than B and the trading periods 3 and 4 ex-hibit a slight upward bias in the average actual exchange price (see Table 1) This provides some slight evidence in favor of the hypothesis

8 Note that the LValrasian hypothesis might lead one to expect a dol~nward bias since excess supply is very large at prices above equilihriuni if sup1)ly is very elastic relative to demand

As a consequence of these considera- tions test 7 was designed specifically to obtain additional information to sup- port or contradict the indicated hypothe- sis In this case as is seen in Chart 7 (see below) buyers rent is substan- tially smaller than sellers rent From the resulting course of contract prices over six trading periods in this experi- ment it is evident that the convergence to equilibrium is very slow From Table 1 the average exchange prices in the last three trading periods are respec- tively $332 $333 and $334 Average contract prices are still exhibiting a grad- ual approach to equilibrium Hence i t is entirely possible that the static equi- librium would eventually have been at- tained A still smaller buyers rent may be required to provide any clear down- ward bias in the static equilibrium One thing however seems quite unmistak- able from Chart 7 the relative magni- tude of buyers and sellers rent affects the speed with which the actual market equilibrium is approached One would expect sellers to present a somewhat weaker bargaining front especially a t first if their rent potential is large rela- tive to that of buyers Thus in Chart 7 i t is seen that several low reservation price sellers in trading periocls 1 and 2 made contracts a t low exchange prices which no doubt seemed quite profit- able to these sellers However in both these trading periods the later exchange prices were much higher revealing to the lour-price sellers that however prof- itable their initial sales had been still greater proLts were possible under stiffer bargaining

-4 stronger test of the hypotheses that buyer and seller rents affect the speed of adjustment and that they affect the final equil1rillln in the market would t)e ohtainal~lc l)j-introclucing actual mon-

etary payoffs in the experiment Thus one might offer to pay each seller the difference between his contract price and his reservation price and each buyer the difference between his reservation price and his contract price In addition one might pay each trader a small lump sum (say $005) just for making a contract in any period This sum would represent

GJeYTITi

iinormal pro~its that is a small return even if the good is sold a t its minimum supply price or purchased a t its maxi- mum demand price The present experi- ments have not seemeti to provide any motivation problems The subjects have shown high motivation to do their best even without monetary payo-tis But our experimental marginal buyers and sellers may be more reluctant to approach their reservation prices than their counter-parts in real markets The use oi nlone-tary payoifs as suggested should remox c

any such reluctance that is attributable to artificial elements in the present cx-peri i~lents ~

The experinlent summarized in Chart 5 was designed to study the effect on market behavior of changes in the condi- tions of demand and supply As it hap- pened this ex1)eriment was performed on a considerably more mature group

T R A N S A C T O N NJMBER ( 3 1 Pi11331

of subjects than any of the other experi- rnents Alost of the experiments were performed on sophornore ant1 junior en-gineering economics and business ma-jors while test 5 was performed on a

Since this was witten an experiment has been tried using monetary payofis and the same supply and demand design shown in Chart 4 The result as conjectured in the text TYas to remove the reluc- tance of sellers to sell at their reservation prices Ey the second trading period the market vas firmly in equilibrium In the thirtl period all trades were at $3ti) Al)parcntly$005 per pcriocl as considerecl satisfactory normal prolit

graduate class in econoinic theory 111

view of this dilference it is most interest- ing to find the phenomenally low values for a exhibited by test 5A The coefficient of convergence is smaller for the opening and later periods of this inarket than for any period of any of the other tests Furthermore trading periods 2-4 show as of less than 1 per cent indicating an inordinately strong and rapid tenden- cy toward equilibrium In this case no offers or bids were accepted until the bidding had converged to prices which were very near indeed to the ecluilibrium Contract prices ranged from $300 to S320 as compared with a possible range from $210 to $375

-It the close of test 5A new cards were distributed correspontling to an increase in demand from DD to DID as shown in Chart 51deg The subjects of course could guess from the fact that new buy- er cards were being distributed that a change in demand was in the wind But they knew nothing of the direction of change in demand except what might be guessed by the buyers from the al- teration of their individual reserv a t ion prices When trading began (period 1 test 5B) the immediate response was a very considerable upward sweep in exchange prices with several contracts being closed in the first trading period well above the new higher ecluilibrium price Indeed the eagerness to buy was so strong that two sellers who were submar- ginal both before and after the increase in demand (their reservation prices were

W o t e also that there was a small (one-unit) decrease in supply from SS to SS This was not planned It was due to the inal~ility of one sul~ject (the seller with the $210 reservation price) in test 5A to participate in test 5B Therefore except for the deletion of this one seller from the market the conditions of supply r e r e not altered that is the scllc~s ol test 5 B retni~~cclthe same rcscrvation 1)ricc cards as they liad ill test 51

$350 and $370) were able to m~bc con- tracts in this transient phase of the mar- ket Consecluently the trading group showing the strongest equilibrating ten- dencies exhibited very erratic behavior in the transient phase following the in- crease in demand Contract prices greatly overshot the new equilibrium and ration- ing by the market was less efficient in this transient phase In the second tratl- ing period of test 5B no submarginal sellers or buyers made contracts and tllc inarket exhibited a narrowed movcment toward the new equilibrium

Test 611 was designed to determine whether market equilibrium was affected by a marlred imbalance between the number of intramarginal sellers and the number of intramarginal buyers near the predicted equilibrium price The demand curve DD in Chart 6 falls continuously to the right in one-unit steps while the supply curve SS becomes perfectly in- elastic a t the price $400 well below the equilibrium price $1075 The tenta- tive hypothesis was that the large rent ($675) enjoyed by the marginal seller with still larger rents for the intramar- ginal sellers might prevent the theoreti- cal equilibrium from being established From the results it is seen that the earlier conjecture concerning the efiect of a divergence between buyer and seller rent on the approach to equilibrium is confirmed The approach to ecluilibrium is from below and the convergence is relatively slow However there is no indication that the lack of marginal sell- ers near the theoretical equilibrium has prevented the equilibrium from being attained The average contract price in trading period 4 is $1090 only $015 above the predicted equilibrium

4t the close of trading period 4 in test 611 thc old buyer cards correspond- ing to DD were rcplaced by new cards

correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

You have printed the following article

An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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[Footnotes]

2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

httplinksjstororgsicisici=0022-38082819480429563A23C953AAEIM3E20CO3B2-V

16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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Page 8: An Experimental Study of Competitive Market Behavior Vernon L. …econ.ucsb.edu/~oprea/176/Competitive.pdf · 2007-09-26 · THE JOURNAL POLITICAL ECONOMY Volume LXX APRIL 1962 Number

Irc- Coef- Ao of Sub Xo of SUE I clicted r~Luill ficient marginalAverage No of Sub- marginal s o of Sub-

Ex- Ex- of Con- H u q e ~ sActual marginal Sellers marginal clrdngc chaigc vergence n h oI ~ ~ ~ l ~ a n g c lloyers ho Sellers Qunn-

t i t y (30)

Quan-t i ty (XI

[a=

(100 un) (Po)I

Could AIaBc

Contractb

Price (r)

Who lade Coritracts

Could M a k e

Con t racts

Viio hladc Colltracts

---- -1-

1 6 5 5 6 3 5 6 5 5 6 7 5 6 6 5

15 16 4 15 15 4 15 16 4

16 17 5 16 5 16 5 16 3

10 None xone None Kone 10 None h-one xone None 10 None None Kone hTone 10 None Kone None None

8 None None None 8 None None None 8 None None None

10 10 10 10

12 12

12 None 12 Kone 12 hone 12 None

None None None None None None None hone Kone hone hTone None

xone None None None xone None

352 103 3 3 2

317 110 4 2 None None 336 3 2 4 1 None Kone 338 2 2 4 0 None None

CHART 2

0 2 4 6 8 10 12 14 16 18 20 2 2 1 4 8 12 17 4 8 12 15 4 O I 15 1 8 i 19

QUANTITY TRAN6ACTiC)N I 4 l i l G F i l I b Y P Rlgtl

excess-rent hypothesis to be discussed later7

The tests in Chart 4 are of special interest from the point of view of the Walrasian hypothesis In this case the supply curve is perfectly elastic-all sell-ers have cards containing the price $310 Each seller has the same lower bound on his reservation price acceptance set

equilibrium since there is a considerable excess supply a t prices just barely above the equilibrium price From the results we see that the market is not particularly slow in converging but i t converges to a fairly stable price about $020 above the predicted equilibrium Furthermore in test 4B which was an extension of 4A the interjection of a decrease in

CHART 4

TEST 4 A AND TEST 48 I6 C O I

- -- --- -580 -560 -5 4 0 - s

520 -

-5 00

Po 1310 Xo10

4 6 0 -

4 2 0 -u

2- 4 3 0 -+DECREASE

3 s o -

3 6 3 -

3 4 0

3 20

300

2 8 0

2 2 0 I

$ 6 0 0

5 80

560

5 4 0

5 2 0

5 0 0

4 80

460

4 4 0

4 20

IN DEMAYD+- O0

3 80

360

3 4 0

3 2 0

- 280

200 1 2 3 4 5 6 7 8 9 10 11 12 1 3 3 5 7 V I 3 5 7 V 1 3 5 7 9 1 3 5 7 9 1 3 5 7 8 1 3 5 7 1 3 5 6

Q ~ I A U T I T Y

In thi5 senie 11erc is no tlivergencc of attitude among the sellers though there might be marked variation in their bar- gaining propensities According to the Walrasian hypothesis this market should exhibit rapid convergence toward the

I T h e results are inconsistent n i t h the so-called hfarshallian hypothesis (the rate of increase in quan- tit) exchanged is an increasing function of the excess of demand price over supply price) but this hy- pothesis nould seem to be worth considering only in market processes in which some quantity-adjust- ing decision is made by the marketers The results of a pilot experiment in short-run and long-run equilibrium are displayed in the Appendix

TRANSACTION NUMBER ( B Y PERIOD1

demand from DD to DID was ineffective as a means of shocking the market down to its supply and demand equilibrium This decrease in demand was achieved by passing out new buyer cards corre- sponding to DD a t the close of period

in test 4A As the market approaches equilibrium from above since contracts a t prices below equilibrium are

The sellers in this market presented 3 solid front against price being lowered to ecluilibrium In the previous mar-

120 VERNON L SYIITFT

kets there was a divergence of seller attitude so that only a very few mar- ginal and near-marginal sellers might offer serious resistance to price being forced to equilibrium And this resistance tended to break down when any of the stronger intramarginal sellers accepted contracts below equilibrium

From these results it is clear that the static competitive market equilibri- um may depend not only on the inter- section of the supply and demanci sched- ules but also upon the shapes of the schedules Specifically I was led from test 4 to the tentative hypothesis that there may be an upward bias in the equilibrium price of a market which will be greater the more elastic is the supply schedule relative to demand8 For example let A be the area under the demand schedule and above the theoreti- cal equilibrium This is Alarshalls con-sumer surplus but to avoid any welfare connotations of this term I shall refer to the area as buyers rent Let B be the area above the supply schedule and below the theoretical equilibrium (Marshalls producer surplus) which I shall call sellers rent Now the tenta- tive hypothesis was that the actual mar- ket ecjuilibrium will be above the the- oretical equilibrium by an amount which depends upon how large A is relative to B Similarly there will be a downward bias if A is small relative to B

Test 4 is of course an extreme case since B = 0 In test 3 A is larger than B and the trading periods 3 and 4 ex-hibit a slight upward bias in the average actual exchange price (see Table 1) This provides some slight evidence in favor of the hypothesis

8 Note that the LValrasian hypothesis might lead one to expect a dol~nward bias since excess supply is very large at prices above equilihriuni if sup1)ly is very elastic relative to demand

As a consequence of these considera- tions test 7 was designed specifically to obtain additional information to sup- port or contradict the indicated hypothe- sis In this case as is seen in Chart 7 (see below) buyers rent is substan- tially smaller than sellers rent From the resulting course of contract prices over six trading periods in this experi- ment it is evident that the convergence to equilibrium is very slow From Table 1 the average exchange prices in the last three trading periods are respec- tively $332 $333 and $334 Average contract prices are still exhibiting a grad- ual approach to equilibrium Hence i t is entirely possible that the static equi- librium would eventually have been at- tained A still smaller buyers rent may be required to provide any clear down- ward bias in the static equilibrium One thing however seems quite unmistak- able from Chart 7 the relative magni- tude of buyers and sellers rent affects the speed with which the actual market equilibrium is approached One would expect sellers to present a somewhat weaker bargaining front especially a t first if their rent potential is large rela- tive to that of buyers Thus in Chart 7 i t is seen that several low reservation price sellers in trading periocls 1 and 2 made contracts a t low exchange prices which no doubt seemed quite profit- able to these sellers However in both these trading periods the later exchange prices were much higher revealing to the lour-price sellers that however prof- itable their initial sales had been still greater proLts were possible under stiffer bargaining

-4 stronger test of the hypotheses that buyer and seller rents affect the speed of adjustment and that they affect the final equil1rillln in the market would t)e ohtainal~lc l)j-introclucing actual mon-

etary payoffs in the experiment Thus one might offer to pay each seller the difference between his contract price and his reservation price and each buyer the difference between his reservation price and his contract price In addition one might pay each trader a small lump sum (say $005) just for making a contract in any period This sum would represent

GJeYTITi

iinormal pro~its that is a small return even if the good is sold a t its minimum supply price or purchased a t its maxi- mum demand price The present experi- ments have not seemeti to provide any motivation problems The subjects have shown high motivation to do their best even without monetary payo-tis But our experimental marginal buyers and sellers may be more reluctant to approach their reservation prices than their counter-parts in real markets The use oi nlone-tary payoifs as suggested should remox c

any such reluctance that is attributable to artificial elements in the present cx-peri i~lents ~

The experinlent summarized in Chart 5 was designed to study the effect on market behavior of changes in the condi- tions of demand and supply As it hap- pened this ex1)eriment was performed on a considerably more mature group

T R A N S A C T O N NJMBER ( 3 1 Pi11331

of subjects than any of the other experi- rnents Alost of the experiments were performed on sophornore ant1 junior en-gineering economics and business ma-jors while test 5 was performed on a

Since this was witten an experiment has been tried using monetary payofis and the same supply and demand design shown in Chart 4 The result as conjectured in the text TYas to remove the reluc- tance of sellers to sell at their reservation prices Ey the second trading period the market vas firmly in equilibrium In the thirtl period all trades were at $3ti) Al)parcntly$005 per pcriocl as considerecl satisfactory normal prolit

graduate class in econoinic theory 111

view of this dilference it is most interest- ing to find the phenomenally low values for a exhibited by test 5A The coefficient of convergence is smaller for the opening and later periods of this inarket than for any period of any of the other tests Furthermore trading periods 2-4 show as of less than 1 per cent indicating an inordinately strong and rapid tenden- cy toward equilibrium In this case no offers or bids were accepted until the bidding had converged to prices which were very near indeed to the ecluilibrium Contract prices ranged from $300 to S320 as compared with a possible range from $210 to $375

-It the close of test 5A new cards were distributed correspontling to an increase in demand from DD to DID as shown in Chart 51deg The subjects of course could guess from the fact that new buy- er cards were being distributed that a change in demand was in the wind But they knew nothing of the direction of change in demand except what might be guessed by the buyers from the al- teration of their individual reserv a t ion prices When trading began (period 1 test 5B) the immediate response was a very considerable upward sweep in exchange prices with several contracts being closed in the first trading period well above the new higher ecluilibrium price Indeed the eagerness to buy was so strong that two sellers who were submar- ginal both before and after the increase in demand (their reservation prices were

W o t e also that there was a small (one-unit) decrease in supply from SS to SS This was not planned It was due to the inal~ility of one sul~ject (the seller with the $210 reservation price) in test 5A to participate in test 5B Therefore except for the deletion of this one seller from the market the conditions of supply r e r e not altered that is the scllc~s ol test 5 B retni~~cclthe same rcscrvation 1)ricc cards as they liad ill test 51

$350 and $370) were able to m~bc con- tracts in this transient phase of the mar- ket Consecluently the trading group showing the strongest equilibrating ten- dencies exhibited very erratic behavior in the transient phase following the in- crease in demand Contract prices greatly overshot the new equilibrium and ration- ing by the market was less efficient in this transient phase In the second tratl- ing period of test 5B no submarginal sellers or buyers made contracts and tllc inarket exhibited a narrowed movcment toward the new equilibrium

Test 611 was designed to determine whether market equilibrium was affected by a marlred imbalance between the number of intramarginal sellers and the number of intramarginal buyers near the predicted equilibrium price The demand curve DD in Chart 6 falls continuously to the right in one-unit steps while the supply curve SS becomes perfectly in- elastic a t the price $400 well below the equilibrium price $1075 The tenta- tive hypothesis was that the large rent ($675) enjoyed by the marginal seller with still larger rents for the intramar- ginal sellers might prevent the theoreti- cal equilibrium from being established From the results it is seen that the earlier conjecture concerning the efiect of a divergence between buyer and seller rent on the approach to equilibrium is confirmed The approach to ecluilibrium is from below and the convergence is relatively slow However there is no indication that the lack of marginal sell- ers near the theoretical equilibrium has prevented the equilibrium from being attained The average contract price in trading period 4 is $1090 only $015 above the predicted equilibrium

4t the close of trading period 4 in test 611 thc old buyer cards correspond- ing to DD were rcplaced by new cards

correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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CHART 2

0 2 4 6 8 10 12 14 16 18 20 2 2 1 4 8 12 17 4 8 12 15 4 O I 15 1 8 i 19

QUANTITY TRAN6ACTiC)N I 4 l i l G F i l I b Y P Rlgtl

excess-rent hypothesis to be discussed later7

The tests in Chart 4 are of special interest from the point of view of the Walrasian hypothesis In this case the supply curve is perfectly elastic-all sell-ers have cards containing the price $310 Each seller has the same lower bound on his reservation price acceptance set

equilibrium since there is a considerable excess supply a t prices just barely above the equilibrium price From the results we see that the market is not particularly slow in converging but i t converges to a fairly stable price about $020 above the predicted equilibrium Furthermore in test 4B which was an extension of 4A the interjection of a decrease in

CHART 4

TEST 4 A AND TEST 48 I6 C O I

- -- --- -580 -560 -5 4 0 - s

520 -

-5 00

Po 1310 Xo10

4 6 0 -

4 2 0 -u

2- 4 3 0 -+DECREASE

3 s o -

3 6 3 -

3 4 0

3 20

300

2 8 0

2 2 0 I

$ 6 0 0

5 80

560

5 4 0

5 2 0

5 0 0

4 80

460

4 4 0

4 20

IN DEMAYD+- O0

3 80

360

3 4 0

3 2 0

- 280

200 1 2 3 4 5 6 7 8 9 10 11 12 1 3 3 5 7 V I 3 5 7 V 1 3 5 7 9 1 3 5 7 9 1 3 5 7 8 1 3 5 7 1 3 5 6

Q ~ I A U T I T Y

In thi5 senie 11erc is no tlivergencc of attitude among the sellers though there might be marked variation in their bar- gaining propensities According to the Walrasian hypothesis this market should exhibit rapid convergence toward the

I T h e results are inconsistent n i t h the so-called hfarshallian hypothesis (the rate of increase in quan- tit) exchanged is an increasing function of the excess of demand price over supply price) but this hy- pothesis nould seem to be worth considering only in market processes in which some quantity-adjust- ing decision is made by the marketers The results of a pilot experiment in short-run and long-run equilibrium are displayed in the Appendix

TRANSACTION NUMBER ( B Y PERIOD1

demand from DD to DID was ineffective as a means of shocking the market down to its supply and demand equilibrium This decrease in demand was achieved by passing out new buyer cards corre- sponding to DD a t the close of period

in test 4A As the market approaches equilibrium from above since contracts a t prices below equilibrium are

The sellers in this market presented 3 solid front against price being lowered to ecluilibrium In the previous mar-

120 VERNON L SYIITFT

kets there was a divergence of seller attitude so that only a very few mar- ginal and near-marginal sellers might offer serious resistance to price being forced to equilibrium And this resistance tended to break down when any of the stronger intramarginal sellers accepted contracts below equilibrium

From these results it is clear that the static competitive market equilibri- um may depend not only on the inter- section of the supply and demanci sched- ules but also upon the shapes of the schedules Specifically I was led from test 4 to the tentative hypothesis that there may be an upward bias in the equilibrium price of a market which will be greater the more elastic is the supply schedule relative to demand8 For example let A be the area under the demand schedule and above the theoreti- cal equilibrium This is Alarshalls con-sumer surplus but to avoid any welfare connotations of this term I shall refer to the area as buyers rent Let B be the area above the supply schedule and below the theoretical equilibrium (Marshalls producer surplus) which I shall call sellers rent Now the tenta- tive hypothesis was that the actual mar- ket ecjuilibrium will be above the the- oretical equilibrium by an amount which depends upon how large A is relative to B Similarly there will be a downward bias if A is small relative to B

Test 4 is of course an extreme case since B = 0 In test 3 A is larger than B and the trading periods 3 and 4 ex-hibit a slight upward bias in the average actual exchange price (see Table 1) This provides some slight evidence in favor of the hypothesis

8 Note that the LValrasian hypothesis might lead one to expect a dol~nward bias since excess supply is very large at prices above equilihriuni if sup1)ly is very elastic relative to demand

As a consequence of these considera- tions test 7 was designed specifically to obtain additional information to sup- port or contradict the indicated hypothe- sis In this case as is seen in Chart 7 (see below) buyers rent is substan- tially smaller than sellers rent From the resulting course of contract prices over six trading periods in this experi- ment it is evident that the convergence to equilibrium is very slow From Table 1 the average exchange prices in the last three trading periods are respec- tively $332 $333 and $334 Average contract prices are still exhibiting a grad- ual approach to equilibrium Hence i t is entirely possible that the static equi- librium would eventually have been at- tained A still smaller buyers rent may be required to provide any clear down- ward bias in the static equilibrium One thing however seems quite unmistak- able from Chart 7 the relative magni- tude of buyers and sellers rent affects the speed with which the actual market equilibrium is approached One would expect sellers to present a somewhat weaker bargaining front especially a t first if their rent potential is large rela- tive to that of buyers Thus in Chart 7 i t is seen that several low reservation price sellers in trading periocls 1 and 2 made contracts a t low exchange prices which no doubt seemed quite profit- able to these sellers However in both these trading periods the later exchange prices were much higher revealing to the lour-price sellers that however prof- itable their initial sales had been still greater proLts were possible under stiffer bargaining

-4 stronger test of the hypotheses that buyer and seller rents affect the speed of adjustment and that they affect the final equil1rillln in the market would t)e ohtainal~lc l)j-introclucing actual mon-

etary payoffs in the experiment Thus one might offer to pay each seller the difference between his contract price and his reservation price and each buyer the difference between his reservation price and his contract price In addition one might pay each trader a small lump sum (say $005) just for making a contract in any period This sum would represent

GJeYTITi

iinormal pro~its that is a small return even if the good is sold a t its minimum supply price or purchased a t its maxi- mum demand price The present experi- ments have not seemeti to provide any motivation problems The subjects have shown high motivation to do their best even without monetary payo-tis But our experimental marginal buyers and sellers may be more reluctant to approach their reservation prices than their counter-parts in real markets The use oi nlone-tary payoifs as suggested should remox c

any such reluctance that is attributable to artificial elements in the present cx-peri i~lents ~

The experinlent summarized in Chart 5 was designed to study the effect on market behavior of changes in the condi- tions of demand and supply As it hap- pened this ex1)eriment was performed on a considerably more mature group

T R A N S A C T O N NJMBER ( 3 1 Pi11331

of subjects than any of the other experi- rnents Alost of the experiments were performed on sophornore ant1 junior en-gineering economics and business ma-jors while test 5 was performed on a

Since this was witten an experiment has been tried using monetary payofis and the same supply and demand design shown in Chart 4 The result as conjectured in the text TYas to remove the reluc- tance of sellers to sell at their reservation prices Ey the second trading period the market vas firmly in equilibrium In the thirtl period all trades were at $3ti) Al)parcntly$005 per pcriocl as considerecl satisfactory normal prolit

graduate class in econoinic theory 111

view of this dilference it is most interest- ing to find the phenomenally low values for a exhibited by test 5A The coefficient of convergence is smaller for the opening and later periods of this inarket than for any period of any of the other tests Furthermore trading periods 2-4 show as of less than 1 per cent indicating an inordinately strong and rapid tenden- cy toward equilibrium In this case no offers or bids were accepted until the bidding had converged to prices which were very near indeed to the ecluilibrium Contract prices ranged from $300 to S320 as compared with a possible range from $210 to $375

-It the close of test 5A new cards were distributed correspontling to an increase in demand from DD to DID as shown in Chart 51deg The subjects of course could guess from the fact that new buy- er cards were being distributed that a change in demand was in the wind But they knew nothing of the direction of change in demand except what might be guessed by the buyers from the al- teration of their individual reserv a t ion prices When trading began (period 1 test 5B) the immediate response was a very considerable upward sweep in exchange prices with several contracts being closed in the first trading period well above the new higher ecluilibrium price Indeed the eagerness to buy was so strong that two sellers who were submar- ginal both before and after the increase in demand (their reservation prices were

W o t e also that there was a small (one-unit) decrease in supply from SS to SS This was not planned It was due to the inal~ility of one sul~ject (the seller with the $210 reservation price) in test 5A to participate in test 5B Therefore except for the deletion of this one seller from the market the conditions of supply r e r e not altered that is the scllc~s ol test 5 B retni~~cclthe same rcscrvation 1)ricc cards as they liad ill test 51

$350 and $370) were able to m~bc con- tracts in this transient phase of the mar- ket Consecluently the trading group showing the strongest equilibrating ten- dencies exhibited very erratic behavior in the transient phase following the in- crease in demand Contract prices greatly overshot the new equilibrium and ration- ing by the market was less efficient in this transient phase In the second tratl- ing period of test 5B no submarginal sellers or buyers made contracts and tllc inarket exhibited a narrowed movcment toward the new equilibrium

Test 611 was designed to determine whether market equilibrium was affected by a marlred imbalance between the number of intramarginal sellers and the number of intramarginal buyers near the predicted equilibrium price The demand curve DD in Chart 6 falls continuously to the right in one-unit steps while the supply curve SS becomes perfectly in- elastic a t the price $400 well below the equilibrium price $1075 The tenta- tive hypothesis was that the large rent ($675) enjoyed by the marginal seller with still larger rents for the intramar- ginal sellers might prevent the theoreti- cal equilibrium from being established From the results it is seen that the earlier conjecture concerning the efiect of a divergence between buyer and seller rent on the approach to equilibrium is confirmed The approach to ecluilibrium is from below and the convergence is relatively slow However there is no indication that the lack of marginal sell- ers near the theoretical equilibrium has prevented the equilibrium from being attained The average contract price in trading period 4 is $1090 only $015 above the predicted equilibrium

4t the close of trading period 4 in test 611 thc old buyer cards correspond- ing to DD were rcplaced by new cards

correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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excess-rent hypothesis to be discussed later7

The tests in Chart 4 are of special interest from the point of view of the Walrasian hypothesis In this case the supply curve is perfectly elastic-all sell-ers have cards containing the price $310 Each seller has the same lower bound on his reservation price acceptance set

equilibrium since there is a considerable excess supply a t prices just barely above the equilibrium price From the results we see that the market is not particularly slow in converging but i t converges to a fairly stable price about $020 above the predicted equilibrium Furthermore in test 4B which was an extension of 4A the interjection of a decrease in

CHART 4

TEST 4 A AND TEST 48 I6 C O I

- -- --- -580 -560 -5 4 0 - s

520 -

-5 00

Po 1310 Xo10

4 6 0 -

4 2 0 -u

2- 4 3 0 -+DECREASE

3 s o -

3 6 3 -

3 4 0

3 20

300

2 8 0

2 2 0 I

$ 6 0 0

5 80

560

5 4 0

5 2 0

5 0 0

4 80

460

4 4 0

4 20

IN DEMAYD+- O0

3 80

360

3 4 0

3 2 0

- 280

200 1 2 3 4 5 6 7 8 9 10 11 12 1 3 3 5 7 V I 3 5 7 V 1 3 5 7 9 1 3 5 7 9 1 3 5 7 8 1 3 5 7 1 3 5 6

Q ~ I A U T I T Y

In thi5 senie 11erc is no tlivergencc of attitude among the sellers though there might be marked variation in their bar- gaining propensities According to the Walrasian hypothesis this market should exhibit rapid convergence toward the

I T h e results are inconsistent n i t h the so-called hfarshallian hypothesis (the rate of increase in quan- tit) exchanged is an increasing function of the excess of demand price over supply price) but this hy- pothesis nould seem to be worth considering only in market processes in which some quantity-adjust- ing decision is made by the marketers The results of a pilot experiment in short-run and long-run equilibrium are displayed in the Appendix

TRANSACTION NUMBER ( B Y PERIOD1

demand from DD to DID was ineffective as a means of shocking the market down to its supply and demand equilibrium This decrease in demand was achieved by passing out new buyer cards corre- sponding to DD a t the close of period

in test 4A As the market approaches equilibrium from above since contracts a t prices below equilibrium are

The sellers in this market presented 3 solid front against price being lowered to ecluilibrium In the previous mar-

120 VERNON L SYIITFT

kets there was a divergence of seller attitude so that only a very few mar- ginal and near-marginal sellers might offer serious resistance to price being forced to equilibrium And this resistance tended to break down when any of the stronger intramarginal sellers accepted contracts below equilibrium

From these results it is clear that the static competitive market equilibri- um may depend not only on the inter- section of the supply and demanci sched- ules but also upon the shapes of the schedules Specifically I was led from test 4 to the tentative hypothesis that there may be an upward bias in the equilibrium price of a market which will be greater the more elastic is the supply schedule relative to demand8 For example let A be the area under the demand schedule and above the theoreti- cal equilibrium This is Alarshalls con-sumer surplus but to avoid any welfare connotations of this term I shall refer to the area as buyers rent Let B be the area above the supply schedule and below the theoretical equilibrium (Marshalls producer surplus) which I shall call sellers rent Now the tenta- tive hypothesis was that the actual mar- ket ecjuilibrium will be above the the- oretical equilibrium by an amount which depends upon how large A is relative to B Similarly there will be a downward bias if A is small relative to B

Test 4 is of course an extreme case since B = 0 In test 3 A is larger than B and the trading periods 3 and 4 ex-hibit a slight upward bias in the average actual exchange price (see Table 1) This provides some slight evidence in favor of the hypothesis

8 Note that the LValrasian hypothesis might lead one to expect a dol~nward bias since excess supply is very large at prices above equilihriuni if sup1)ly is very elastic relative to demand

As a consequence of these considera- tions test 7 was designed specifically to obtain additional information to sup- port or contradict the indicated hypothe- sis In this case as is seen in Chart 7 (see below) buyers rent is substan- tially smaller than sellers rent From the resulting course of contract prices over six trading periods in this experi- ment it is evident that the convergence to equilibrium is very slow From Table 1 the average exchange prices in the last three trading periods are respec- tively $332 $333 and $334 Average contract prices are still exhibiting a grad- ual approach to equilibrium Hence i t is entirely possible that the static equi- librium would eventually have been at- tained A still smaller buyers rent may be required to provide any clear down- ward bias in the static equilibrium One thing however seems quite unmistak- able from Chart 7 the relative magni- tude of buyers and sellers rent affects the speed with which the actual market equilibrium is approached One would expect sellers to present a somewhat weaker bargaining front especially a t first if their rent potential is large rela- tive to that of buyers Thus in Chart 7 i t is seen that several low reservation price sellers in trading periocls 1 and 2 made contracts a t low exchange prices which no doubt seemed quite profit- able to these sellers However in both these trading periods the later exchange prices were much higher revealing to the lour-price sellers that however prof- itable their initial sales had been still greater proLts were possible under stiffer bargaining

-4 stronger test of the hypotheses that buyer and seller rents affect the speed of adjustment and that they affect the final equil1rillln in the market would t)e ohtainal~lc l)j-introclucing actual mon-

etary payoffs in the experiment Thus one might offer to pay each seller the difference between his contract price and his reservation price and each buyer the difference between his reservation price and his contract price In addition one might pay each trader a small lump sum (say $005) just for making a contract in any period This sum would represent

GJeYTITi

iinormal pro~its that is a small return even if the good is sold a t its minimum supply price or purchased a t its maxi- mum demand price The present experi- ments have not seemeti to provide any motivation problems The subjects have shown high motivation to do their best even without monetary payo-tis But our experimental marginal buyers and sellers may be more reluctant to approach their reservation prices than their counter-parts in real markets The use oi nlone-tary payoifs as suggested should remox c

any such reluctance that is attributable to artificial elements in the present cx-peri i~lents ~

The experinlent summarized in Chart 5 was designed to study the effect on market behavior of changes in the condi- tions of demand and supply As it hap- pened this ex1)eriment was performed on a considerably more mature group

T R A N S A C T O N NJMBER ( 3 1 Pi11331

of subjects than any of the other experi- rnents Alost of the experiments were performed on sophornore ant1 junior en-gineering economics and business ma-jors while test 5 was performed on a

Since this was witten an experiment has been tried using monetary payofis and the same supply and demand design shown in Chart 4 The result as conjectured in the text TYas to remove the reluc- tance of sellers to sell at their reservation prices Ey the second trading period the market vas firmly in equilibrium In the thirtl period all trades were at $3ti) Al)parcntly$005 per pcriocl as considerecl satisfactory normal prolit

graduate class in econoinic theory 111

view of this dilference it is most interest- ing to find the phenomenally low values for a exhibited by test 5A The coefficient of convergence is smaller for the opening and later periods of this inarket than for any period of any of the other tests Furthermore trading periods 2-4 show as of less than 1 per cent indicating an inordinately strong and rapid tenden- cy toward equilibrium In this case no offers or bids were accepted until the bidding had converged to prices which were very near indeed to the ecluilibrium Contract prices ranged from $300 to S320 as compared with a possible range from $210 to $375

-It the close of test 5A new cards were distributed correspontling to an increase in demand from DD to DID as shown in Chart 51deg The subjects of course could guess from the fact that new buy- er cards were being distributed that a change in demand was in the wind But they knew nothing of the direction of change in demand except what might be guessed by the buyers from the al- teration of their individual reserv a t ion prices When trading began (period 1 test 5B) the immediate response was a very considerable upward sweep in exchange prices with several contracts being closed in the first trading period well above the new higher ecluilibrium price Indeed the eagerness to buy was so strong that two sellers who were submar- ginal both before and after the increase in demand (their reservation prices were

W o t e also that there was a small (one-unit) decrease in supply from SS to SS This was not planned It was due to the inal~ility of one sul~ject (the seller with the $210 reservation price) in test 5A to participate in test 5B Therefore except for the deletion of this one seller from the market the conditions of supply r e r e not altered that is the scllc~s ol test 5 B retni~~cclthe same rcscrvation 1)ricc cards as they liad ill test 51

$350 and $370) were able to m~bc con- tracts in this transient phase of the mar- ket Consecluently the trading group showing the strongest equilibrating ten- dencies exhibited very erratic behavior in the transient phase following the in- crease in demand Contract prices greatly overshot the new equilibrium and ration- ing by the market was less efficient in this transient phase In the second tratl- ing period of test 5B no submarginal sellers or buyers made contracts and tllc inarket exhibited a narrowed movcment toward the new equilibrium

Test 611 was designed to determine whether market equilibrium was affected by a marlred imbalance between the number of intramarginal sellers and the number of intramarginal buyers near the predicted equilibrium price The demand curve DD in Chart 6 falls continuously to the right in one-unit steps while the supply curve SS becomes perfectly in- elastic a t the price $400 well below the equilibrium price $1075 The tenta- tive hypothesis was that the large rent ($675) enjoyed by the marginal seller with still larger rents for the intramar- ginal sellers might prevent the theoreti- cal equilibrium from being established From the results it is seen that the earlier conjecture concerning the efiect of a divergence between buyer and seller rent on the approach to equilibrium is confirmed The approach to ecluilibrium is from below and the convergence is relatively slow However there is no indication that the lack of marginal sell- ers near the theoretical equilibrium has prevented the equilibrium from being attained The average contract price in trading period 4 is $1090 only $015 above the predicted equilibrium

4t the close of trading period 4 in test 611 thc old buyer cards correspond- ing to DD were rcplaced by new cards

correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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120 VERNON L SYIITFT

kets there was a divergence of seller attitude so that only a very few mar- ginal and near-marginal sellers might offer serious resistance to price being forced to equilibrium And this resistance tended to break down when any of the stronger intramarginal sellers accepted contracts below equilibrium

From these results it is clear that the static competitive market equilibri- um may depend not only on the inter- section of the supply and demanci sched- ules but also upon the shapes of the schedules Specifically I was led from test 4 to the tentative hypothesis that there may be an upward bias in the equilibrium price of a market which will be greater the more elastic is the supply schedule relative to demand8 For example let A be the area under the demand schedule and above the theoreti- cal equilibrium This is Alarshalls con-sumer surplus but to avoid any welfare connotations of this term I shall refer to the area as buyers rent Let B be the area above the supply schedule and below the theoretical equilibrium (Marshalls producer surplus) which I shall call sellers rent Now the tenta- tive hypothesis was that the actual mar- ket ecjuilibrium will be above the the- oretical equilibrium by an amount which depends upon how large A is relative to B Similarly there will be a downward bias if A is small relative to B

Test 4 is of course an extreme case since B = 0 In test 3 A is larger than B and the trading periods 3 and 4 ex-hibit a slight upward bias in the average actual exchange price (see Table 1) This provides some slight evidence in favor of the hypothesis

8 Note that the LValrasian hypothesis might lead one to expect a dol~nward bias since excess supply is very large at prices above equilihriuni if sup1)ly is very elastic relative to demand

As a consequence of these considera- tions test 7 was designed specifically to obtain additional information to sup- port or contradict the indicated hypothe- sis In this case as is seen in Chart 7 (see below) buyers rent is substan- tially smaller than sellers rent From the resulting course of contract prices over six trading periods in this experi- ment it is evident that the convergence to equilibrium is very slow From Table 1 the average exchange prices in the last three trading periods are respec- tively $332 $333 and $334 Average contract prices are still exhibiting a grad- ual approach to equilibrium Hence i t is entirely possible that the static equi- librium would eventually have been at- tained A still smaller buyers rent may be required to provide any clear down- ward bias in the static equilibrium One thing however seems quite unmistak- able from Chart 7 the relative magni- tude of buyers and sellers rent affects the speed with which the actual market equilibrium is approached One would expect sellers to present a somewhat weaker bargaining front especially a t first if their rent potential is large rela- tive to that of buyers Thus in Chart 7 i t is seen that several low reservation price sellers in trading periocls 1 and 2 made contracts a t low exchange prices which no doubt seemed quite profit- able to these sellers However in both these trading periods the later exchange prices were much higher revealing to the lour-price sellers that however prof- itable their initial sales had been still greater proLts were possible under stiffer bargaining

-4 stronger test of the hypotheses that buyer and seller rents affect the speed of adjustment and that they affect the final equil1rillln in the market would t)e ohtainal~lc l)j-introclucing actual mon-

etary payoffs in the experiment Thus one might offer to pay each seller the difference between his contract price and his reservation price and each buyer the difference between his reservation price and his contract price In addition one might pay each trader a small lump sum (say $005) just for making a contract in any period This sum would represent

GJeYTITi

iinormal pro~its that is a small return even if the good is sold a t its minimum supply price or purchased a t its maxi- mum demand price The present experi- ments have not seemeti to provide any motivation problems The subjects have shown high motivation to do their best even without monetary payo-tis But our experimental marginal buyers and sellers may be more reluctant to approach their reservation prices than their counter-parts in real markets The use oi nlone-tary payoifs as suggested should remox c

any such reluctance that is attributable to artificial elements in the present cx-peri i~lents ~

The experinlent summarized in Chart 5 was designed to study the effect on market behavior of changes in the condi- tions of demand and supply As it hap- pened this ex1)eriment was performed on a considerably more mature group

T R A N S A C T O N NJMBER ( 3 1 Pi11331

of subjects than any of the other experi- rnents Alost of the experiments were performed on sophornore ant1 junior en-gineering economics and business ma-jors while test 5 was performed on a

Since this was witten an experiment has been tried using monetary payofis and the same supply and demand design shown in Chart 4 The result as conjectured in the text TYas to remove the reluc- tance of sellers to sell at their reservation prices Ey the second trading period the market vas firmly in equilibrium In the thirtl period all trades were at $3ti) Al)parcntly$005 per pcriocl as considerecl satisfactory normal prolit

graduate class in econoinic theory 111

view of this dilference it is most interest- ing to find the phenomenally low values for a exhibited by test 5A The coefficient of convergence is smaller for the opening and later periods of this inarket than for any period of any of the other tests Furthermore trading periods 2-4 show as of less than 1 per cent indicating an inordinately strong and rapid tenden- cy toward equilibrium In this case no offers or bids were accepted until the bidding had converged to prices which were very near indeed to the ecluilibrium Contract prices ranged from $300 to S320 as compared with a possible range from $210 to $375

-It the close of test 5A new cards were distributed correspontling to an increase in demand from DD to DID as shown in Chart 51deg The subjects of course could guess from the fact that new buy- er cards were being distributed that a change in demand was in the wind But they knew nothing of the direction of change in demand except what might be guessed by the buyers from the al- teration of their individual reserv a t ion prices When trading began (period 1 test 5B) the immediate response was a very considerable upward sweep in exchange prices with several contracts being closed in the first trading period well above the new higher ecluilibrium price Indeed the eagerness to buy was so strong that two sellers who were submar- ginal both before and after the increase in demand (their reservation prices were

W o t e also that there was a small (one-unit) decrease in supply from SS to SS This was not planned It was due to the inal~ility of one sul~ject (the seller with the $210 reservation price) in test 5A to participate in test 5B Therefore except for the deletion of this one seller from the market the conditions of supply r e r e not altered that is the scllc~s ol test 5 B retni~~cclthe same rcscrvation 1)ricc cards as they liad ill test 51

$350 and $370) were able to m~bc con- tracts in this transient phase of the mar- ket Consecluently the trading group showing the strongest equilibrating ten- dencies exhibited very erratic behavior in the transient phase following the in- crease in demand Contract prices greatly overshot the new equilibrium and ration- ing by the market was less efficient in this transient phase In the second tratl- ing period of test 5B no submarginal sellers or buyers made contracts and tllc inarket exhibited a narrowed movcment toward the new equilibrium

Test 611 was designed to determine whether market equilibrium was affected by a marlred imbalance between the number of intramarginal sellers and the number of intramarginal buyers near the predicted equilibrium price The demand curve DD in Chart 6 falls continuously to the right in one-unit steps while the supply curve SS becomes perfectly in- elastic a t the price $400 well below the equilibrium price $1075 The tenta- tive hypothesis was that the large rent ($675) enjoyed by the marginal seller with still larger rents for the intramar- ginal sellers might prevent the theoreti- cal equilibrium from being established From the results it is seen that the earlier conjecture concerning the efiect of a divergence between buyer and seller rent on the approach to equilibrium is confirmed The approach to ecluilibrium is from below and the convergence is relatively slow However there is no indication that the lack of marginal sell- ers near the theoretical equilibrium has prevented the equilibrium from being attained The average contract price in trading period 4 is $1090 only $015 above the predicted equilibrium

4t the close of trading period 4 in test 611 thc old buyer cards correspond- ing to DD were rcplaced by new cards

correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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etary payoffs in the experiment Thus one might offer to pay each seller the difference between his contract price and his reservation price and each buyer the difference between his reservation price and his contract price In addition one might pay each trader a small lump sum (say $005) just for making a contract in any period This sum would represent

GJeYTITi

iinormal pro~its that is a small return even if the good is sold a t its minimum supply price or purchased a t its maxi- mum demand price The present experi- ments have not seemeti to provide any motivation problems The subjects have shown high motivation to do their best even without monetary payo-tis But our experimental marginal buyers and sellers may be more reluctant to approach their reservation prices than their counter-parts in real markets The use oi nlone-tary payoifs as suggested should remox c

any such reluctance that is attributable to artificial elements in the present cx-peri i~lents ~

The experinlent summarized in Chart 5 was designed to study the effect on market behavior of changes in the condi- tions of demand and supply As it hap- pened this ex1)eriment was performed on a considerably more mature group

T R A N S A C T O N NJMBER ( 3 1 Pi11331

of subjects than any of the other experi- rnents Alost of the experiments were performed on sophornore ant1 junior en-gineering economics and business ma-jors while test 5 was performed on a

Since this was witten an experiment has been tried using monetary payofis and the same supply and demand design shown in Chart 4 The result as conjectured in the text TYas to remove the reluc- tance of sellers to sell at their reservation prices Ey the second trading period the market vas firmly in equilibrium In the thirtl period all trades were at $3ti) Al)parcntly$005 per pcriocl as considerecl satisfactory normal prolit

graduate class in econoinic theory 111

view of this dilference it is most interest- ing to find the phenomenally low values for a exhibited by test 5A The coefficient of convergence is smaller for the opening and later periods of this inarket than for any period of any of the other tests Furthermore trading periods 2-4 show as of less than 1 per cent indicating an inordinately strong and rapid tenden- cy toward equilibrium In this case no offers or bids were accepted until the bidding had converged to prices which were very near indeed to the ecluilibrium Contract prices ranged from $300 to S320 as compared with a possible range from $210 to $375

-It the close of test 5A new cards were distributed correspontling to an increase in demand from DD to DID as shown in Chart 51deg The subjects of course could guess from the fact that new buy- er cards were being distributed that a change in demand was in the wind But they knew nothing of the direction of change in demand except what might be guessed by the buyers from the al- teration of their individual reserv a t ion prices When trading began (period 1 test 5B) the immediate response was a very considerable upward sweep in exchange prices with several contracts being closed in the first trading period well above the new higher ecluilibrium price Indeed the eagerness to buy was so strong that two sellers who were submar- ginal both before and after the increase in demand (their reservation prices were

W o t e also that there was a small (one-unit) decrease in supply from SS to SS This was not planned It was due to the inal~ility of one sul~ject (the seller with the $210 reservation price) in test 5A to participate in test 5B Therefore except for the deletion of this one seller from the market the conditions of supply r e r e not altered that is the scllc~s ol test 5 B retni~~cclthe same rcscrvation 1)ricc cards as they liad ill test 51

$350 and $370) were able to m~bc con- tracts in this transient phase of the mar- ket Consecluently the trading group showing the strongest equilibrating ten- dencies exhibited very erratic behavior in the transient phase following the in- crease in demand Contract prices greatly overshot the new equilibrium and ration- ing by the market was less efficient in this transient phase In the second tratl- ing period of test 5B no submarginal sellers or buyers made contracts and tllc inarket exhibited a narrowed movcment toward the new equilibrium

Test 611 was designed to determine whether market equilibrium was affected by a marlred imbalance between the number of intramarginal sellers and the number of intramarginal buyers near the predicted equilibrium price The demand curve DD in Chart 6 falls continuously to the right in one-unit steps while the supply curve SS becomes perfectly in- elastic a t the price $400 well below the equilibrium price $1075 The tenta- tive hypothesis was that the large rent ($675) enjoyed by the marginal seller with still larger rents for the intramar- ginal sellers might prevent the theoreti- cal equilibrium from being established From the results it is seen that the earlier conjecture concerning the efiect of a divergence between buyer and seller rent on the approach to equilibrium is confirmed The approach to ecluilibrium is from below and the convergence is relatively slow However there is no indication that the lack of marginal sell- ers near the theoretical equilibrium has prevented the equilibrium from being attained The average contract price in trading period 4 is $1090 only $015 above the predicted equilibrium

4t the close of trading period 4 in test 611 thc old buyer cards correspond- ing to DD were rcplaced by new cards

correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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graduate class in econoinic theory 111

view of this dilference it is most interest- ing to find the phenomenally low values for a exhibited by test 5A The coefficient of convergence is smaller for the opening and later periods of this inarket than for any period of any of the other tests Furthermore trading periods 2-4 show as of less than 1 per cent indicating an inordinately strong and rapid tenden- cy toward equilibrium In this case no offers or bids were accepted until the bidding had converged to prices which were very near indeed to the ecluilibrium Contract prices ranged from $300 to S320 as compared with a possible range from $210 to $375

-It the close of test 5A new cards were distributed correspontling to an increase in demand from DD to DID as shown in Chart 51deg The subjects of course could guess from the fact that new buy- er cards were being distributed that a change in demand was in the wind But they knew nothing of the direction of change in demand except what might be guessed by the buyers from the al- teration of their individual reserv a t ion prices When trading began (period 1 test 5B) the immediate response was a very considerable upward sweep in exchange prices with several contracts being closed in the first trading period well above the new higher ecluilibrium price Indeed the eagerness to buy was so strong that two sellers who were submar- ginal both before and after the increase in demand (their reservation prices were

W o t e also that there was a small (one-unit) decrease in supply from SS to SS This was not planned It was due to the inal~ility of one sul~ject (the seller with the $210 reservation price) in test 5A to participate in test 5B Therefore except for the deletion of this one seller from the market the conditions of supply r e r e not altered that is the scllc~s ol test 5 B retni~~cclthe same rcscrvation 1)ricc cards as they liad ill test 51

$350 and $370) were able to m~bc con- tracts in this transient phase of the mar- ket Consecluently the trading group showing the strongest equilibrating ten- dencies exhibited very erratic behavior in the transient phase following the in- crease in demand Contract prices greatly overshot the new equilibrium and ration- ing by the market was less efficient in this transient phase In the second tratl- ing period of test 5B no submarginal sellers or buyers made contracts and tllc inarket exhibited a narrowed movcment toward the new equilibrium

Test 611 was designed to determine whether market equilibrium was affected by a marlred imbalance between the number of intramarginal sellers and the number of intramarginal buyers near the predicted equilibrium price The demand curve DD in Chart 6 falls continuously to the right in one-unit steps while the supply curve SS becomes perfectly in- elastic a t the price $400 well below the equilibrium price $1075 The tenta- tive hypothesis was that the large rent ($675) enjoyed by the marginal seller with still larger rents for the intramar- ginal sellers might prevent the theoreti- cal equilibrium from being established From the results it is seen that the earlier conjecture concerning the efiect of a divergence between buyer and seller rent on the approach to equilibrium is confirmed The approach to ecluilibrium is from below and the convergence is relatively slow However there is no indication that the lack of marginal sell- ers near the theoretical equilibrium has prevented the equilibrium from being attained The average contract price in trading period 4 is $1090 only $015 above the predicted equilibrium

4t the close of trading period 4 in test 611 thc old buyer cards correspond- ing to DD were rcplaced by new cards

correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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correspoilding to UL) in Chart 6 Trad-ing was resumed with the new conditions of decreased demand (test 6B) There was not sufficient time to permit two full trading periods of market experience to be obtained under the new demand conditions However from the results i11 Chart 6 i t is evident that the market responded promptly to the decrease in

(test 8 A ) only sellers were permittecl to enunciate offers In this market buyers played a passive role they could either accept or reject the offers of sellers but were not permitted to make bids This market was intended to simulate sp-proximately an ordinary retail market In such markets in the United States sellers typically take the initiative in

CHART 8

demand by showing apparent conver-gence to the new equilibrium Note in particular that there occurred no signifi- cant tendency for market prices to over- shoot the new equilibrium as was ob-served in test 5B

All of the above experiments were con- ducted under the same general rules of market organization Test 8 was per-formed as an exploratory means of test- ing the effect of changes in market or- ganization on market price In the first four trading periods of this experiment

advertising their offer prices with buyers electing to buy or not to buy rather than taking part in a higgling and bar- gaining process Since sellers desire to sell a t the highest prices they can get one would expect the offer prices to be high and consequently one might ex-pect the exchange prices to show a per- sistent tendency to remain above the predicted equilibrium The result was in accordance with this crude expectation in the first market period only (test 8A Chart 8) Since sellers only were making

ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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ESPERTRIETII STUDY OF COMPETITIVE MARKET BEH4VIOR 123

offers the price quotations tended to be very much above equilibrium Five of these offers mere accepted a t prices ranging from $269 to $280 by the five buyers with maximum reservation prices of $273 or more This left only buyers with lower reservation prices The com- petition of sellers pushed the offer prices lower and the remaining buyers made contracts a t prices ($235 $200 and $200) near or below the equilibrium price The early buyers in that first mar- ket period never quite recovered from having subsequently seen exchange prices fall much below the prices a t which they had bought Having been badly fleeced through ignorance in that first trading period they refrained from accepting any high price offers in the remaining three periods of the test This action together with seller offer price competi- tion kept exchange prices a t levels per- sistently below equilibrium for the re-mainder of test 8A Furthermore the coefficient of convergence increased from 29 per cent in the second trading period to 74 and 70 per cent in the last two periods At the close of the fourth trading period the market rules were changed to allow buyers to make quotations as well as sellers Under the new rules (test 8B) two trading periods were run Ex- change prices immediately moved toward equilibrium with the closing prices of period 1 and opening prices of period 2 being above the equilibrium for the first time since period 1 of test 8A

I t would seem to be of some signifi- cance that of the ten experiments re-ported on test 8 shows the clearest lack of convergence toward equilibrium More -experiments are necessary to confirm or

deny these but it appearthat important changes in market or-ganization-such as permitting only sell- ers make quotations-have a distinct-ly disturbing effcct on the equilibrating

process I n particular the conclusion is suggested that markets in which only sellers competitively publicize their offers tend to operate to the benefit of buyers a t the expense of sellers

Turning to tests 9A and 10 (shown in Charts 9 and lo) i t should be noted that the buyers and sellers in these tests received the same cards as their counter- parts in test 7 The only difference was that the former entered the market to effect two transactions each instead of one Thus the three buyers with $370 cards could each buy two units a t $370 or less in tests 9 and 10 This change in the design of test 7 resulted in a doubling of the maximum demand and supply quantities a t each hypothetical price

By permitting each buyer and seller to make two contracts per period twice as much market experience is poten- tially to be gained by each trader in a given period Each trader can experiment more in a given market-correcting his bids or offers in the light of any surprises or disappointments resulting from his first contract In the previous experi- ments such corrections or alterations in the bargaining behavior of a trader had to await the next trading period once the trader had made a contract

l1 This process of correction over time based upon observed price quotations and the actual con- tracts that are executed is the underlying adjust- ment mechanism operating in all of these experi- ments This is in contrast with the LValrasian titon-nement or groping process in which when a price is cried and the effective demand and offer corre- sponding to this price are not equal another price is cried for which there is another corresponding effective demand and offer (see Leon Walras Ele-mens of Pure Economics trans LVilliam Jaffe [Chi- cago Richard D Iruin Inc 19541 p 242) The 1Valrasian groping process suggests a centralized institutional means of trying different price quota- tions until the equilibrium is discovered In our experiments as in real markets the groping process is decentralized with all contracts binding whether they are at equilibrium or non-equili1rrirlm prices

126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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126 -ERNON L SXIITII

Comparison of the results of the three trading periods in test 9A with the first three trading periods of test 7 shows that the tendencies toward equilibrium (as measured by a ) were greater in test 9A during the first two periods and small- er in the third period The same com- parison between tests 7 and 10 reveals a stronger tendency toward equilibrium in test 10 than in the first three periods

of trade increased to the new equilibrium rate of twenty units per period Note that the equilibrium tendency in the trading period of test 9B was greater than in any of the perious periods of test 9A The increase in demand far from destabilizing the market as was the case in test 5B tended to strengthen its relatively weak ecluilibrium tenden- cies

CHART 9

of 7 TTence a n increase in vclume appears to sleetl the equilibrating process In- tleed the three trading periods of test 10 are roughly equivalent to the six trading periods of test 7 so that doubling s-olume in a given period is comparable to running two trading periods a t the same volume

I n test 9B the consequences of an in- crease in demand were once again tested Contract prices responded by moving upward immediately and the volume

IV EMPIRICAL ANALYSIS OF EXPERI-

MENTAL DATA THE EXCESS-

RENT HYPOTHESIS

The empirical analysis of these ten experiments rests upon the hypothesis that there exists a stochastic difference equation which best represents the price convergence tendencies apparent in Charts 1-10 The general hypothesis is that Apt = p t + ~- pt =[~l (p t )

xz(pgt I + E l ( 1 )

EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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EXPERIMENTAL STUDY OF COLIPETITIVE SIARKET BEfI-iVIOR 127

where the arguments XI xs reflect characteristics of the experimental sup- ply and demand curves and the bar- gaining characteristics of individual test groups and e t is a random variable with zero mean For a given experimental test group untler the so-called Walrasian hypothesis xl(pt) might be the excess demand prevailing a t pt withf = 0 when x1 = 0

My first empirical investigation is con- cerned with the measuremet of the equi- librating tendencies in these markets and the ability of supply and demand theory to predict the equilibrium price in each experiment To this end note that equa- tion (1) defines a stochastic phase func- tion12 of the form pt+l = g(pr) + el An equilibrium price Po is attained when P = g(Po) Rather than estimate the

phase function for each experiment it was found convenient to make linear estimates of its first difference that is

The corresponding linear phase function has slope 1 + al The parameters ao and al were estimated by linear regression techniques for each of the ten funda-mental experiments and are tabulated in column 1 of Table 213 Confidence

I2 See for example W J Baumol Economic Dynamics (Bew York hiacmillan Co 1959) pp 257-65

3 The least squares estimate of a1 in these experi- ments can be expected to be biased (see L Hurwicz Least-Squares Bias in Time Series chap xv in T Koopmans Statistical Infererzce i n Dy~zamic Eco- nomic Alfodels [Sew York John Wiley amp Sons 19501) Hovever since in all of the basic experiments there are twenty or more observations the bias ~vill not tend to be large

- OFFERS 0 - BIDS 0 - OFFERS ACCEPTED A - BIDS ACCEPTED

--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

You have printed the following article

An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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This article references the following linked citations If you are trying to access articles from anoff-campus location you may be required to first logon via your library web site to access JSTOR Pleasevisit your librarys website or contact a librarian to learn about options for remote access to JSTOR

[Footnotes]

2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

httplinksjstororgsicisici=0022-38082819480429563A23C953AAEIM3E20CO3B2-V

16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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--

intervals for a 95 per cent fiducial proba- bility level are shown in parentheses un- der the estimate of al for each experiment With the exception of experiment SA the 95 per cent confidence interval for each regression coefficient is entirely contained in the interval -2 lt a1 lt 0 which is recluired for market stability Hence of these ten experin~ents SA is the only one whose price movements are sufli-ciently erratic to prevent us from reject- ing the null hypothesis of instability and of the ten basic experiments this

u u + alP0[ = - -

Y (au+al I u )

for the sample estimates on the assump- tion that Apt = 0 when p t = Po in the population These t-values are shown in column 1 Table 3 for the ten primary and the five B auxilary experiments Low absolute values of t imply that relative to the error in the prediction the predicted equilibrium is close to the theoretical The four lowest absolute t-values are for experimental designs with the smallest difference between equilibri-

TABLE 3

I I I I

is the one in which the trading rules were altered to permit only sellers to quote prices14

The regressions of column 1 Table 2 and associated computation provide a means of predicting the adjustment pressure on price Apt for any given pLI n particular we can compute

T h ~ e e of the five auxiliary B experiments demonstratccl a similar instability (in the iiducial probabilii- sense) but the samples were consider- a l ~ l y sn~aller than their 4 counterparts they I-eprese~itedconsitlerahly fewer trading periods and they hat1 tliricrent ant1 val-ying objectives Thc un- stable ones el-e 4 B 8B and 9B

um buyers and sellers rent These re- sults provide some additional evidence in favor of our conjecture in Part 111 that the equilibrium is influenced by the relative sizes of the areas A and B However from the t-values i t would seem that the influence is small except for test 4 where B = 0 In this case the null hypothesis (Apt = 0 when pt = PO) is rejected even a t a significance level below 005

Four specific forms for the difference ecluation (1) were studied in detail and tested for their ability to predict the

theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

You have printed the following article

An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

httplinksjstororgsicisici=0022-38082819620429703A23C1113AAESOCM3E20CO3B2-J

This article references the following linked citations If you are trying to access articles from anoff-campus location you may be required to first logon via your library web site to access JSTOR Pleasevisit your librarys website or contact a librarian to learn about options for remote access to JSTOR

[Footnotes]

2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

httplinksjstororgsicisici=0022-38082819480429563A23C953AAEIM3E20CO3B2-V

16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

httpwwwjstororg

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theoretical cc~uilil~rium 1)rice rll~ese will be referred to as the Walrasian the es- cess-rent the modified Walrasian and the modified excess-rent hypotheses re- spectively The 4alrasian hypothesis is Apt = Pol + Pllxlt where xlt is the ex-cess deinand prevailing a t the price p a t which the fth transaction occurred Because of the conjecture that buy-ers and sellers rent might have an ef- fect on iildividual and marliet adjust-ment an excess-rent hypothesis was in- troduced This hypothesis is Apt = jS02 + $22n21~vlicre m e t is the alqcl~raic area

1)et~veen the supply and demand curves and extends from the eiluilihrium price down to the price of the tth transaction as sho~vn in Figure 1 The modified Val- rasian hypothesis is Apt = Poa + P13xLt+ Pasxat where m a t = A ) - By the al- gebraic difference l ~ e t ~ v e e ~ the ecluilibri- um buyers rent A ant1 the ecluilibriurn sellers rent Bf The motivation here was to introduce a term in the adjust- ment equation which would permit the actual equilibriunl price to be biased above or below the theoretical equilibri- um by an amount proportional to the algebraic difference bctivccn buycrs lnd

sellers rent a t the tlieoretical ccluilil~li- urn I t was believed that such a general hypothesis might be necessary to account for the obvious price equilibrium bias in experiment 4 and the slight apparent bias in experiments 3 611 7 and 9A -1similar motivation suggested the modi- fied excess-rent hypothesis Ap = po4+ P 4 2 2 1 + P34~3t

Since the trading process in these e l -periments was such that transactions might and generally did take place a t non-equilibrium prices the supply and demand curves shift after each transac- tion Hence in generating observation5 on xlt xzt and xal the supply and de- illand curves were adjusted after each transaction for the effect of the pairing of a buyer and a seller in reducing their elfective demand and supply Thus in Chart 7 the first transaction was a t S050 between the seller with reservation 1)rice $020 and a buyer with reservation rice $Z50 1ollo~ving this trasaction the

new effective demand and supply curves I~ecoineDd and ss as shown The next transaction is a t $150 Our hypothesis is that the increase in price from $050 to $150 is due to the conditions repre- sented by Dd and ss a t the price $050 Thus for the first set of observations Apl = $1 -Po = $150 -$050 = $100 xll = 11 xzl= 2010 and XBI = -960 as can be determined from Chart 7 lhc second transaction paired a $ZiO buycr and a $060 seller The next set of obse~ -

vations is then obtained by removing this buyer and seller from Dd and ss to obtain x12 x2 and x3 a t $2 = 150 with ApL= p2-pl = 0 and so on

Using observations obtained in this manner regressions for the four different equilibrating hypotheses were computetl for the ten fundamental experiments as shown in Table 2 columns 2-5 1 95 pcr cent co~ifidence interval is sllui~ 11 ill

EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

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An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

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16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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EXPERIIENTL STCDY 01CORZPETITIVE MARKET RETIVIOR 151

l~trcntheses under each regression coeffi- ing thereby to support the excess-rent cient With the exception of experiment hypothesis - inore exact discrimin 1011t 1

811 the regression coefficients for every experiment are sigrlificant under both the Iaalrasian and the excess-rent hy-potheses On the other hand 333 in the modified 17alrasian hypothesis is signifi- cant only in experiment 2 In none of the experiments is Paqsignificant for the modified excess-rent hypothesis These highly unambiguous results seem to sug- gest that little significance can be at-tached to the effect of a difference be- tween equilibrium buyers and sellers rent in biasing the price equilibrium ten- dencies

On this reasoning we are left with the closely competing Malrasian and ex- cess-rcnt hypotheses showing highly sig- nificant adjustment speeds and 022 In cliscriminating between these two hy- potheses we shall compare them on two important counts (1) their ability to predict zero price change in equilibrium and (2) the standard errors of said pre- dictions Since x = x = 0 in equilibri- um this requires a comparison between the absolute values of the intercepts of the Walrasian and the excess-rent re-gressions pol and P o 2 and between S(Po) and S(PU2) Under the first com-parison we can think of 1 Pol1 shown in column 2 Table 3 as a score for the IValrasian hypothesis and Po21 shown in column 5 as a score for the excess- relit hypothesis - low intercept repre- sents a good score Thus for experiment 1 in ecluilibriuin there is a residual tend- ency for price to change (in this case fall) a t the rate of 26 cents per transac- tion by the Walrasian and 28 cents by the excess-rent regressions - casual comparison of columns 2 and 5 reveals that in most of the experiments I Pol1 gt 1 Po)and in those for which the reverse is true the diifererlcc is cluite small tend-

can be lllade by applying the Wilcoxon paired-sample rank test for related Sam- ples to the scores of columns 2 and 5 This test applies to the difierences I pol 1 - I Po1 and tests the null hypothe- sis IIothat the UTalrasian and excess- rent alternatives are equivalent (the tlis- trihution of the differences is symmetric about zero) If applied to all the experi- ments including the Bs (-V = 15) II is rejected a t the lt 02 significance level The difference between our paired series of scores in favor of the er~cess- rent hypothesis is therefore signiiicant I t is highly debatable whether all the experiments should he included in such a test especially 4 which did not tend to the predicted equilibriun~ 8 which represented a different organization of the bargaining and possibly the B ex-periments where the samples were smail Therefore the test was run omitting all these experiments (Y = 8) giving a re- jection of Iloa t the 05 la-el Omitting only 4 and 8 (LV= 11) allowed 11still to he rejected a t the lt 02 level

If we compare the standard errors S(Po1) and S(P02) in Table 3 colui~lns 3 and 6 we see that again the excess-rent hypothesis tends to score higher (smaller standard errors) Applying the Wilcoxoll test to S(Pol) - S(Po2) for all the experi- ments (AV= 151 we find that this cliffer- ence in favor of the excess-rent hypothc- sis is significant a t the lt O1 level The difference is still significant a t the lt O1 level if we omit 4 and 8 from the test and it is significant a t the 05 level if we also eliminate all the B esperi-ments

The t-values for the two hypotheses

l5 See for example K IBroivnlce Statisiictil T l r c o i ~ nrzd lTcti~odi~log~ 12iigiiiecriizgi r z Sciocc-c tat i t l

(Yew York John ilcy amp Solis 19GO) 111) 196-99

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

You have printed the following article

An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

httplinksjstororgsicisici=0022-38082819620429703A23C1113AAESOCM3E20CO3B2-J

This article references the following linked citations If you are trying to access articles from anoff-campus location you may be required to first logon via your library web site to access JSTOR Pleasevisit your librarys website or contact a librarian to learn about options for remote access to JSTOR

[Footnotes]

2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

httplinksjstororgsicisici=0022-38082819480429563A23C953AAEIM3E20CO3B2-V

16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

httpwwwjstororg

LINKED CITATIONS- Page 1 of 1 -

NOTE The reference numbering from the original has been maintained in this citation list

Page 21: An Experimental Study of Competitive Market Behavior Vernon L. …econ.ucsb.edu/~oprea/176/Competitive.pdf · 2007-09-26 · THE JOURNAL POLITICAL ECONOMY Volume LXX APRIL 1962 Number

132 VERNON LSLIITH

are shown in columris 4 and 7 of Table 3 They tend also to be lower for the excess-rent hypothesis

Bearing in mind that our analysis is based upon a limited number of experi- ments and that revisions may be re-quired in the light of further experiments with different subjects or with monetary payoffs we conclude the following Of the four hypotheses tested the two modi- fied forms show highly insignificant re-gression coefficients for the added ex-planatory variable As between the Wal- rasian and the excess-rent hypotheses the evidence is sharply in favor of the latter

V 1lt1TIONALIZ4TION O F THE EXCESS-

RENT HYPOTHESIS

Having provided a tentative empirical verification of the hypothesis that price in a competitve (auction) market tends to rise or fall in proportion to the excess buyer plus seller rent corresponding to any contract price it remains to provide some theoretical rationale for such a hy- pothesis From the description of the above experiments and their results the excess-rent hypothesis would seem to have some plausibility from an individ- ual decision-making point of view Given that a particular contract price has just been executed it is reasonable to expect each trader to compare that price with his own reservation price the difference being a profit or rent which he con- siders achievable and to present a degree oi bargaining resistance in the auction process which is greater the smaller is this rent Such resistance may tend to give way even where the rents on one side or the otlier are very small ii it be- comes clear that such rents are unattain- able Thus if equilibrium buyers rent erccetls sellers rcnt any curly tendency lor contract prices to reiliain a b o ~ e eilui-

librium (and balance the rents achieved on both sides) might be expected to break down as it becomes evident that the paper rents a t those prices may not be attainable by all of the sellers By this argument it is suggested that the propensity of sellers to reduce their offers when price is above equilibrium is related to their attempts to obtain some-even if a smallH-amount of rent rather than to a direct influence of excess supply

A particularly interesting aspect of the excess-rent hypothesis is that it leads naturally to an interesting optimality interpretation of the static competitive market equilibrium The principle is this in static equilibrium a competitive mar- ket minimizes the total virtual rent re- ceived by buyers and sellers By virtual rent I mean the rent that would be enjoyed if all buyers and sellers could be satisfied a t any given disequilibrium price To see this optimality principle let D(p) be the demand function and S(p) the supply function At p = P the sum of buyer and seller virtual rent is

and is represented by the area from

in Figure 1 R is a minimum for normal supply and demand functions when

that is when demand equals supply with P = PONote particularly that there is nothing artificial about this conversion of the statement of an ordinary competi- tive market equilibrium into a corre-sponding minimum problem Whether one desires to attach any welfare sig- nificance to the concepts of consumer and producer surplus or not i t is corn-

1 up to SSand fro111 PD D down to

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

You have printed the following article

An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

httplinksjstororgsicisici=0022-38082819620429703A23C1113AAESOCM3E20CO3B2-J

This article references the following linked citations If you are trying to access articles from anoff-campus location you may be required to first logon via your library web site to access JSTOR Pleasevisit your librarys website or contact a librarian to learn about options for remote access to JSTOR

[Footnotes]

2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

httplinksjstororgsicisici=0022-38082819480429563A23C953AAEIM3E20CO3B2-V

16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

httpwwwjstororg

LINKED CITATIONS- Page 1 of 1 -

NOTE The reference numbering from the original has been maintained in this citation list

Page 22: An Experimental Study of Competitive Market Behavior Vernon L. …econ.ucsb.edu/~oprea/176/Competitive.pdf · 2007-09-26 · THE JOURNAL POLITICAL ECONOMY Volume LXX APRIL 1962 Number

EXPERIMENTAL STUDY OF COT

pletely plausible to require in the in- terests of strict market efficiency that no trader be imputed more rent than is absolutely necessary to perform the exchange mechanics Hence a t price P in Figure 1virtual rent exceeds equilibri- um rent and if this price persists some sellers get more rent than they should

I t should perhaps be pointed out that the excess-rent and Walrasian hypothe- ses are close analogues in that both deal with virtual unattainable quanti- ties Thus under the Walrasian hypothe- sis the virtual excess supply a t P in Figure 1 is unattainable Indeed i t is this fact that presumably causes price to fall Similarly a t P the excess rent area above S and D is unattainable and leads to price cutting Also note that the Walrasian hypothesis bears a gradient relationship while the excess-rent hypothesis shows a global adjusting relationship to the rent minimization principle At P gt Po the Walrasian hy- pothesis says that price tends to fall a t a time rate which is proportional to the marginal rent dRdP a t that price The excess-rent hypothesis states that price tends to fall a t a time rate which is proportional to the global dif- ference between total rent a t P and a t Po

Samuelson has shown how one may convert the Cournot-Enke problem of spatial price equilibrium into a maximum problem16 The criterion to be maximized in a single market would be what he calls social payoff defined as the al-gebraic area under the excess-demand curve In spatially separated markets the criterion is to maximize net social payoff defined as the sum of the social payoffs in all regions minus the total transport costs of all interregional ship-

A Samuelson Spatial Price Equilibrium and Linear Programming American Econonzir I-lip X1II (June 1952) 284-92

ments But according to Samuelson (this magnitude is artificial in the sense that noVcomDetitor in the market will be aware of or concerned with it I t is artificial in the sense that after an In- visible Hand has led us to its maxi- mization we need not necessarily attach any social welfare significance to the re- sult I think the formulation of compe- titive market equilibrium as a rent mini- mization problem makes the Invisible Hand distinctly more visible and more t e l e~ log ica l ~~ has socialIt also great (though not necessarily welfare) signifi- cance in relation to Lfrictionless market efficiency Rent is an unearned incre-ment which literally cries out for mini- mization in an efficient economic organi- zation Furthermore as we have seen with the excess-rent and Walrasian hy- potheses both the abstract teleological goal of the competitive market and the dynamics of its-tamptonnement process are branches of the same market mecha-nism

In view of the electrical circuit ana- logue so often mentioned in connection with spatially separated markets a final bonus of the minimum rent formulation is the fact that i t represents a more direct analogy with the principle of mini- mum heat loss in electric circuitslg Na- ture has devised a set of laws to govern the flow of electrical energy which it

l7 Ibid p 288

l8 The discovery of the excess-rent hypothesis draws me nearer to the camp of Invisible Hand enthusiasts but only because of the greater visibility of the Hand I cannot quite carry my market metaphysics as far as does Samuelson I t is well known that any problem in economic equilibrium can be converted into a maximum (or minimum) problem but I question the value of such a trans- formation (beyond technical advantages) if it is purely artificial without any meaningful interpreta- tion and if we work at it such a meaningful tmns- formation may often be found

can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

You have printed the following article

An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

httplinksjstororgsicisici=0022-38082819620429703A23C1113AAESOCM3E20CO3B2-J

This article references the following linked citations If you are trying to access articles from anoff-campus location you may be required to first logon via your library web site to access JSTOR Pleasevisit your librarys website or contact a librarian to learn about options for remote access to JSTOR

[Footnotes]

2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

httplinksjstororgsicisici=0022-38082819480429563A23C953AAEIM3E20CO3B2-V

16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

httpwwwjstororg

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NOTE The reference numbering from the original has been maintained in this citation list

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can be shown minimizes the inefficient wasteful loss of heat energy from electri- cal systems Similarly the market mech- anism provides a set of laws which minimizes the wasteful payment of excessive economic rent

VI SUhlMAKY

I t would be premature to assert any broad generalizations based upon the ten experiments we have discussed Yet con- clusions are important for purposes of specifying the exact character of any findings whether those findings are ulti- mately verified or not In this spirit the following tentative conclusions are offered concerning these experiments

1 Even where numbers are small there are strong tendencies for a supply and demand competitive equilibrium to be attained as long as one is able to prohibit collusion and to maintain ab- solute publicity of all bids offers and transactions Publicity of quotations and absence of collusion were major charac- teristics of these experimental markets

2 Changes in the conditions of supply or demand cause changes in the volume of transactions per period and the general level of contract prices These latter cor- respond reasonably well with the pre- dictions of competitive price theory The response to such changes may however produce a transient phase of very erratic contract price behavior

3 Some slight evidence has been pro-

vided to suggest that a prediction of the static equilibrium of a competitive mar- ket requires knowledge of the shapes of the supply and demand schedules as well as the intersection of such schedules The evidence is strongest in the extreme case in which the supply curve is per- fectly elastic with the result that the empirical equilibrium is higher than the theoretical equilibrium

4 Markets whose institutional organi- zation is such that only sellers make price quotations may exhibit weaker equilibri- um tendencies than markets in which both buyers and sellers make price quota- tions-perhaps even disequilibrium tend- encies Such one-sided markets may op- erate to the benefit of buyers A possible explanation is that in the price-formation process buyers reveal a minimum of in- formation concerning their eagerness to buy

5 The so-called Walrasian hypothe- sis concerning the mechanism of market adjustment seems not to be confirmed A more adequate hypothesis is the ex- cess-rent hypothesis which relates the speed of contract price adjustment to the algebraic excess of buyer plus seller virtual rent over the equilibrium buyer plus seller rent This new hy-pothesis becomes particularly intriguing in view of the fact that a competitive market for a single commodity can be interpreted as seeking to minimize total rent

APPENDIX

In the course of this experimental study and its analysis several additional or periph- eral issues were investigated a discussion of which would not fit clearly into the main body of this report Three such issues will be discussed briefly in this appendix for the benefit of readers interested in some of the numerous additional lines of inquiry that might be pursued

I EVIDENCE OF IKTER-TRiDIKG-PERIOD

LEARNIKG

In testing the various equilibrating hy- potheses under investigation in this paper no attempt was made to distinguish the effects of different trading periods The sam- ple of observations for each experiment em- braced all the trading periods of that ex-

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

You have printed the following article

An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

httplinksjstororgsicisici=0022-38082819620429703A23C1113AAESOCM3E20CO3B2-J

This article references the following linked citations If you are trying to access articles from anoff-campus location you may be required to first logon via your library web site to access JSTOR Pleasevisit your librarys website or contact a librarian to learn about options for remote access to JSTOR

[Footnotes]

2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

httplinksjstororgsicisici=0022-38082819480429563A23C953AAEIM3E20CO3B2-V

16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

httpwwwjstororg

LINKED CITATIONS- Page 1 of 1 -

NOTE The reference numbering from the original has been maintained in this citation list

Page 24: An Experimental Study of Competitive Market Behavior Vernon L. …econ.ucsb.edu/~oprea/176/Competitive.pdf · 2007-09-26 · THE JOURNAL POLITICAL ECONOMY Volume LXX APRIL 1962 Number

puiment with transactions running continu- sioiis may be better equilibrating equations ously from the first trading period through (better predictors of zero price change when the last I t would appear however that excess rent is zero) than the earlier period learning occurs as the experiment progresses regressions in sucli a way as to alter the parameters of each equilibrating hypothesis from one 11 CONVERGENCE OF BID OFFER

trading period to the next T o obtain some A S D CONTRACT PRICES

idea of the extent of these alterations re- I n experiments 9 and 10 a tape-recorder gressions for the excess-rent hypothesis mere was used for the first time to obtain a record conlputed by individual trading period for of all bid and offer prices as well as the tests 6A 9 d and 10 These regression equa- contract prices KO analysis has as yet been tions are summarized in Table 4 I t is evi- attempted with these additional data How- dent that there is a tendency for the inter- ever a graph of the bid offer and contract cepts of these regressions to converge toward prices in their serial sequence of occurrence zero as the number of trading periods in- is suggestive Such a sample graph is shown creases Convergence of the intercepts sug- in Chart 11 for experiment 10 Perhaps gebtb that the later trading period regres- the most interesting fact revealed in this

TABLE 4

EXCESS-RENT A p t = 8 0 2 f PERIODREGRESSIONS B z X 2 t BY TRADING Trading Icriod Experiment 6h Experiment 9h Experiment 10

1 -2769+0101 x y t -0335+0078 xri -0160f0087 zi 2 -2876f0216 ~ 2 6 -0148+0001 xrl -0053+0408 ~ 2 t

3 0273+0029 r 2 t -0191f0093 x ~ t 0007+0349 x r t

4 0121f0391 X Z ~

CIIXRI 11

~ l u s OIIER~AND TRANSACT~ONS OX msr 10

T E S T 10 1

8

Po= $340 X o = 13

L I

- 3 2 -

i

I I

I I

i i

0 2 R 6 8 10 I2 14 16 18 20 22 24 26 28 1 5 11 1 5 1 8 3 7 11 1 7 3 7 11 1

QUANTITY TRANSACTICN IIUIIGER (BY P E R I Z C I

410

chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

You have printed the following article

An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

httplinksjstororgsicisici=0022-38082819620429703A23C1113AAESOCM3E20CO3B2-J

This article references the following linked citations If you are trying to access articles from anoff-campus location you may be required to first logon via your library web site to access JSTOR Pleasevisit your librarys website or contact a librarian to learn about options for remote access to JSTOR

[Footnotes]

2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

httplinksjstororgsicisici=0022-38082819480429563A23C953AAEIM3E20CO3B2-V

16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

httpwwwjstororg

LINKED CITATIONS- Page 1 of 1 -

NOTE The reference numbering from the original has been maintained in this citation list

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chart is the apparent tendency for the vari- ance of the bids and offers to stabilize early +it11 the contract prices continuing to con- verge Tithin thii variation in bids and offers ~h~~ it is at the begillIlillg Of 1 up to about the eighth transaction that the bids offers seem to shoJ$7 the most pro- nounamp variation This variation the11 re- mains reasonably steady to the very end of the last trading period Co~ltract prices

III A PILOT EXPERIMENT IN SHOK~-RUN

AND [LONG-RUN EQulLIBRIunf

An important characteristic of the ten experiments discussed in this paper was the absence of any qualltity-adjusting de- cision-making behavior 011the part of either buyers or sellers Such experiments repre- sent the simulation of markets for commodi- ties which do not have to be delivered or

CHlIltl 12

TEST 11

QUANTITY

converge but the traders continue to at- tempt to get better terms by making re-peatedly high offers and low bids In this connection note that the unaccepted offers are further above the contract prive level than the unaccepted bids are below the contract price level Similar results were evident in a corresponding chart (not shown) for experiment 9 This apparently is the auction markets way of compensating for the fact that in this particular experiment seller were i l l a iofter (higher rent) 1)osi- tion than buyer

TRANSACTION NUMBER ( B Y PERIOD1

even produced until after the sale contract is executed Hence the possibility of distress sales leading to losses by sellers is ruled out by experinlental design I n long-run price theory we think of producers entering or leaving an industry in response to the profits or losses they expect to make The results of one pilot experiment to simulate this process is shown in Chart 12 The significant nen element in this evperinlent war giving all sellers the option a t the beginning of each trading period of eiiteriiig the ~narliet or remaining out of produc-

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

You have printed the following article

An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

httplinksjstororgsicisici=0022-38082819620429703A23C1113AAESOCM3E20CO3B2-J

This article references the following linked citations If you are trying to access articles from anoff-campus location you may be required to first logon via your library web site to access JSTOR Pleasevisit your librarys website or contact a librarian to learn about options for remote access to JSTOR

[Footnotes]

2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

httplinksjstororgsicisici=0022-38082819480429563A23C953AAEIM3E20CO3B2-V

16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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Page 26: An Experimental Study of Competitive Market Behavior Vernon L. …econ.ucsb.edu/~oprea/176/Competitive.pdf · 2007-09-26 · THE JOURNAL POLITICAL ECONOMY Volume LXX APRIL 1962 Number

EXPERIMEXTL4L STUDY OF CO3IPETITIVE K4RKET BEHL4VIOR 137

tion I t was understood that if they en-tered the market it was a t a cost equal to the price on their card and this cost 1val a net lois to any seller failing to make a s~e llso in this experiment some sellers vere producers of two units and some of one unit Specifically there were six sellers nith one unit and five with two units Similarly some buyers were two-unit buyers and some were one-unit buyers I t was not knonn to the traders generally how many or who were traders in one or in two units This procedure was employed primarily to prevent traders from having exact knowl- edge of short-run supply by simply counting the number of sellers in the market in any trading period Buyers in particular were thereby faced with some uncertainty to temper their knowledge that sellers were under strong selling pressure once they en- tered the market

The experiment was conducted over five trading periods In period 1 two sellers with a capacity to produce three units (the $475 and S300 sellers in Chart 12) elected to

remain out of production They were market observers only Therefore the period 1 ihort- run theoretical supply was perfectly inelastic a t Sl = 13 In period 2 only the S450 seller who sold a t a loss the firqt time remained out giving Sz = 15 In period 3 the $500 and $450 sellers remained out giving S3= 14 and in periods 4 and i production stabilized with the $500 S150 and S425 producers out of the m~trhet giving S4= S5= 12

From the results is it clear that this market approaches its long-run equilibri- um price $450 more slo-ly than was the case in the previous experinents The ap- proach is from below as might be expected by the distress sale characteristic of the market The pressure on producers to sell seems to have had its strongest erfect in period 1 in which market prices tended to decline from their opening Prices moved erratically in period 2 and in the remaining periods climbed steadily in the direction of equilibrium

You have printed the following article

An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

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[Footnotes]

2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

httplinksjstororgsicisici=0022-38082819480429563A23C953AAEIM3E20CO3B2-V

16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

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Page 27: An Experimental Study of Competitive Market Behavior Vernon L. …econ.ucsb.edu/~oprea/176/Competitive.pdf · 2007-09-26 · THE JOURNAL POLITICAL ECONOMY Volume LXX APRIL 1962 Number

You have printed the following article

An Experimental Study of Competitive Market BehaviorVernon L SmithThe Journal of Political Economy Vol 70 No 2 (Apr 1962) pp 111-137Stable URL

httplinksjstororgsicisici=0022-38082819620429703A23C1113AAESOCM3E20CO3B2-J

This article references the following linked citations If you are trying to access articles from anoff-campus location you may be required to first logon via your library web site to access JSTOR Pleasevisit your librarys website or contact a librarian to learn about options for remote access to JSTOR

[Footnotes]

2 An Experimental Imperfect MarketEdward H ChamberlinThe Journal of Political Economy Vol 56 No 2 (Apr 1948) pp 95-108Stable URL

httplinksjstororgsicisici=0022-38082819480429563A23C953AAEIM3E20CO3B2-V

16 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

17 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

19 Spatial Price Equilibrium and Linear ProgrammingPaul A SamuelsonThe American Economic Review Vol 42 No 3 (Jun 1952) pp 283-303Stable URL

httplinksjstororgsicisici=0002-82822819520629423A33C2833ASPEALP3E20CO3B2-W

httpwwwjstororg

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