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NBER WORKING PAPER SERIES
REAL BUSINESS CYCLES: A NEW KEYNESIAN PERSPECTIVE
N. Gregory Mankiw
Working Paper No. 2882
NATIONAL BUREAU OF ECONOMIC RESEARCH1050 Massachusetts Avenue
Cambridge, MA 02138March 1989
Professor of Economics, Harvard University, and Research Associate, NationalBureau of Economic Research. This paper was prepared for the Journal ofEconomic Persyectives. I am grateful to Laurence Ball, Susanto Basu,Marianne Baxter, Mark Bils, Lawrence Katz, Deborah Mankiw, David Romer,Joseph Stiglitz, Lawrence Summers, Timothy Taylor, David Weil, and MichaelWoodford, for helpful discussions and comments, and to the National ScienceFoundation for financial support. This paper is part of NBER's researchprograms in Economic Fluctuations and in Financial Markets and MonetaryEconomics. Any opinions expressed are those of the author not those of theNational Bureau of Economic Research.
NBER Working Paper #2882March 1989
REAL BUSINESS CYCLES: A NEW KEYNESIAN PERSPECTIVE
ABSTRACT
This paper is a critique of the latest new classical theory of
economic fluctuations. According to this theory, the business cycle
is the natural and efficient response of the economy to exogenous changes
in the available production technology. This paper discusses several
versions of this theory and argues that this line of research is unlikely
to yield an empirically plausible explanation of observed economic
fluctuations.
N. Cregory MankiwNational Bureau of Economic Research1050 Massachusetts AvenueCambridge, MA 02138
the aftermath
the Great Dep
The debate over the source and propagati
fluctuations rages as fiercely today as it di
of Keynes's The Theory
ression. Today, there
ssical school es the
actors, the a of re
demand, and iency
nesian schoo s that
ons requires study
rium, but als ating
The cia
economic
supply and
The Key
fluctuati
thought
private
equate
markets.
economic
of general
market fai
Real
classical
on of economj
d fifty years
and in the mi
are two schoo
optimization
lative prices
of unfettered
understand in
ing the intri
the possibil
C
ago in
dst of
is of
of
to
g
cacies
ity of
as then,
emphas iz
dj ustment
the effic
1 believe
not just
0 appreci
scale.
theory is the
fluctuations.
e qu
lure
bus
view
ii ib
on a grand
mess cycle
of economic
late
It
are large
change.
rationally
The busine
efficient
product i o
My
in the rate of
these fluctuations, i
levels of labor supply
according to this theo
the ec
random fluctuations
n response to
alter their
ss cycle is,
response of
n technology.
goal in this essay
approach to the business cyc
St incarnation of the
assumes that there
technological
ndividuals
and consumption.
ry, the natural and
onomy to changes in the available
am not an advocate.
is
le
In my view,
to appraise this
I should admit
real business
not provide an
fluctuations
empir
Zoth
ically plaus
its reliance
newly revived
in advance that I
cycle theory does
of economic
ogical
ible expi
on large
1
anat ion
technol
disturbances as the primary source of economic fluctuations and
its reliance on the intertemporal substitution of leisure to
explain changes in employment are fundamental weaknesses.
Moreover, to the extent that it trivializes the social cost of
observed fluctuations, real business cycle theory is potentially
dangerous. The danger is that those who advise policy-makers
might attempt to use it to evaluate the effects of alternative
macroeconomic policies or to conclude that macroeconomic policies
are unnecessary.
Wairasian Equilibrium and The Classical Dichotomy
The typical undergraduate course in microeconomics begins
with partial equilibrium analysis of individual markets. A
market for a good is characterized by a downward sloping demand
curve and an upward sloping supply curve. The price of the good
is assumed to adjust until the quantity supplied equals the
quantity demanded.
The course then builds up to Wairasian general equilibrium.
In this Wairasian equilibrium, prices adjust to equate supply and
demand in every market simultaneously. The general equilibrium
system determines the quantities of all goods and services sold
and their relative prices. The most important theoretical
result, after the existence of such a Wairasian equilibrium, is
the "invisible hand" theorem: the equilibrium is Pareto
efficient.
Courses in microeconomics thus show how employment.
2
g money in t
tinkin 1956)
ative prices,
by the Ja1ras
ce level, the nomi
then determined by
since nominal van
arket is not very
suggests that, fo
The profe
class ical
librium,
either
Real variables, such as
including the real inte
jan system. Nominal
nal wage, and the nom
the equilibrium in t
The
money
nd
evel of
employment,
rest rate,
production, and relative
mention of the existence
simplest way to append in
demand function and an e
depends on the level of
prices are determined without any
of money, the medium of exchange.
oney to the model is to specify a
xogenous morey supply. Money dema
output and the price level. The 1
output is already determined in the
level, however, can adjust to equat
Walrasian system.
e supply and demand
money market.
Introduc in
dichotomy. (Pa
output, and tel
are determined
The price
in the
his way leads to the classical
as
rat
Of
the
the
mar
the
e,
cou
ec
ke t
pri
are
rse
ney m
onomy
can be ignored
var j
inal
he in
t real
lass ic
uss ion
ables
impor
r mos
do
tant
t po
ables
inte
oney
var i
al vi
s, th
not affec
This c
licy disc
such
rest
market.
ables
ew of
e money
the
equi
must
with
ssor of macroeconomic
dichotomy. Given th
money is largely irre
destroy this classical
s must in some way deal with
e assumptions of Walrasian
levant. The macroeconomjst
dichotomy or learn to live
it
Keynesian macroeconomics destroys the classical dichotomy by
abandoning the assumption that wages and prices adjust instantly
to clear markets. This approach is motivated by the observation
3
chat many nominal wages are fixed by long-term labor contracts
and many product prices remain unchanged for long periods of
time. Once the inflexibility of wages and prices is admitted
into a macroeconomic model, the classical dichotomy and the
irrelevance of money quickly di
of the early
attempted to
the fundamen
sappear
Much work in the new classical revolution of
the l970s destroy the classical dichotomy without
abandoning tal axiom of continuous market clearing.
(Lucas 1972,1973) These models were based on the assumption that
individuals have imperfect information regarding prices. These
individuals therefore confuse movements in the overall price
level (which under the classical dichotomy should not matter)
with movements in relative prices (which should matter). An
unanticipated decrease in the money supply leads individuals to
infer that the relative prices of the goods they produce are
temporarily low, which induces them to reduce the quantity
supplied. TJhile the fascination with this sort of story was
substantial in the l970s, it has attracted relatively few
adherents in the 1980s. It is hard to believe that confusion
about the price level is sufficiently great to generate the large
changes in quantities observed over the business cycle.
In contrast to both the Keynesian and the early new
classical approaches to the business cycle, real business cycle
theory embraces the classical dichotomy. It accepts the complete
irrelevance of monetary policy,
by almost all macroeconomists a
thereby denying a tenet accepted
decade ago. Nominal variables,
4
such as the money supply and the price level, are assumed to have
no role in explaining fluctuations in real variables, such as
output and employment.
Real business cycle theory thus pushes the Walrasian model
farther than it has been pushed before. In evaluating whether it
provides a successful explanation of recessions and booms, two
questions naturally arise. First, why are there such large
fluctuations in output and employment? And second, why do
movements in nominal variables, such as the money supply, appear
related to movements in real variables, such as output?
Classical and Keynesian Views of Economic Fluctuations
The only forces that can cause economic fluctuations,
according to real business cycle theory, are those forces that
change the Wairasian equilibrium. The Walrasian equilibrium is
simply the set of quantities and relative prices that
simultaneously equate supply and demand in all markets in the
economy. To understand how real business cycle theory explains
the business cycle, it is necessary to look into the fundamental
forces that change the supplies and demands for various goods and
services
Many sorts of macroeconomic disturbances can in principle
generate fluctuations in real business cycle models. For
example, changes in the level of government purchases or in the
investment tax credit alter the demand for goods and therefore
affect the WaIrasian equilibrium. Changes in the relative price
5
of oil alter the equilibrium allocation of labor among
alternative uses. Many of the macroeconomic disturbances that
receive much attention among Keynesian macroeconomists will also
have important effects in real business cycle models. There is,
however, substantial disagreement between the two schools
regarding the mechanisms through which these disturbances work.
Consider the case of a temporary increase in government
purchases. Almost all macroeconomists agree that such a change
causes an increase in output and employment, and the evidence,
mainly from wartime experience, supports this prediction. Yet
the explanations of this effect of government purchases differ
greatly. (Cf. Barro 1987 and Dornbusch and Fischer 1987)
Real business cycle theory emphasizes the intertemporal
substitution of goods and leisure. It begins by pointing out
that an increase in government purchases increases the demand for
goods. To achieve equilibrium in the goods market, the real
interest rate must rise, which reduces consumption and
investment. The increase in the real interest rate also causes
individuals to reallocate leisure across time. In particular, at
a higher real interest rate, working today becomes relatively
more attractive than working in the future; today's labor supply
therefore increases. This increase in labor supply causes
equilibrium employment and output to rise.
While Keynesian theory also predicts an increase in the real
interest rate in response to a temporary increase in government
purchases, the effect of the real interest rate on labor supply
6
market is charac
• Inc
theory
oyment.
Both real busi
conclude that incre
and employment
imp 1 i cation s
Wairasian mod
observational
with both the
increase in
in the amount of
Keynesian theory, the
state of excess
y thus
output
minent
emp oral
rox ima te
are consistent
The Cen
Wh
princ ip
mode
The
gen
act
bus
dir
fal
tral
ile
le cause
used on technologic
of disturbances ar
business cycle mode
is that over
sure move in
into a reces
economy goes
al disturbances.
e unlikely to
Is that resemble
the typical
opposite
sion, consumption
into a boom,
does not play a crucial role. Instead, the
employment and output is due to a reduction
labor unemployed or underutilized. In most
labor
supply
cycle
unemp I
ontrast
does not
terized as
the Wa].ras
allow for
of
ian
the
ten in a
approach of
possibility
real bus
of invol
mes s
untary
ness cycle theory and Keynesian theor
ases in government purchases increase
This example shows that some of the pro
Keynesian models also come Out of intert
Macroeconomists face a problem of app
of
els
eq
ci
uivalen
assical
Ce: many ob
and Keynes
served phenomena
ian paradigms.
many sorts of macroeconomic disturbances
economic fluctuations in real busine
can
ss c
in
ycle
ls, most attention has foc
reason is that other sorts
erate fluctuations in real
ual economic fluctuations.
An obvious but important fact
mess cycle, consumption and lei
ections. When the economy goes
Is and leisure rises. When the
7
increase in government purchases,
should fall. Many other changes
a change due to a temporary inves
cause consumption and leisure to
Real business cycle theo
recession find it rational to
they demand at the same time
they demand. The answer mu
relative to goods, the real
crucial implication of real
real wage is procyclical.1
If the production function w
were the source of fluctuations,
abor and
roduction
produce a
real, wage
and leisure
goods, such as
also should
iduals in
leisure
of goods
ure
Hence
C the
cons
is p
cons
s inc
ump t
0 tCfl
urnp t
e bo
Lon
tia
ion
th
rises and leisur
lly problematic f
and leisure woul
are normal goods.
e falls. Explaining t
or real business cycle
d often be expected to
In the example of a
his p
theo
move
t emp 0
henome non
ry:
together.
rary
both consumpt
in the demand
tment tax cred
move together.
ion
for
it,
ry must explain why mdiv
increase the quantity of
they decrease the quantity
st be that the price of leis
wage, falls in a recession.
business cycle theory is tha
a
a
generating a p
in a recession
ere unchanging and demand shocks
real business cycle theory would
rocyc I
one
have tro
input is
product
unchang i
labor wo
procyci i
uble
low
of 1
ng p
uld
cal
ical real wage. S
would expect that
ince labor
the marginal
thus the real wage should be high. With an
function, diminishing marginal returns to
countercyclical real wage, not the
necessary to explain the fluctuations in
'Alternatively, one could explain the observed patternwithout a procyclical real wage by positing that tastes forconsumption relative to leisure varyover time. Recessions arethen periods of "chronic laziness." As far as I know, no one hasseriously proposed this explanation of the business cycle.
8
ure.
ycle
tua t
theorists
ions in the
there
rate
fore
of
assume that
technological
there
change
and leis
usiness c
tial fluc
ion, th
The
In
reduce
real bus
5 as a c
uations
and the
of emplo
Attempts
e available production
marginal product of
response to the low
consumption and inc
mess cycle theory
hanging Walrasian e
are efficient. Civ
technological p055
yment, output, and
by the government
market, such as policies
technology is relatively
labor and thus the real
return to working,
rease leisure.
describes economic
quilibrium, it implies that
en the tastes of
ibilities facing society,
consumption
Real b
are substan
In a recess
unfavorable
wage are low
individuals
Since
fluc tuat ion
these fluct
individuals
the levels
improved.
the private
best are me
"invisible h
Of all
optimalicy
It seems un
recession t
explains th
coordinatjo
ffective and
consumption
to alter the
to stabilize
by iat worst can do harm
cannot be
allocations of
employment, at
mpeding the
and
the
of e
deni
han
N
implicatconomic f
able that
in the bo
ions of real business
luctuations is perhaps
the level of welfare
om that preceded it.
cycle theory, the
the most shocking.
is lower in a
Keynesian theory
e in economic
adjust
tion in welfare by a failur
use wages and prices do not
e reduc
n: beca
taneously to
from trade go
ss cycle theo
welfare is 1
ins tan
gains
bus me
reason
equate supply and demand in all markets, s
unrealized in a recession. In contrast,
ry allows no unrealized gains from trade.
ower in a recessiqn is, according to these
9
ome
real
The
theories, that the technological capabilities of society have
declined.
Advocates
convincing ske
sudden changes
that the accum
cycle theorists
run fluctuation
Edward Pr
the importance
changes in tot
economy- - the p
inputs, where
shares. This
technological
substantial El
suggests a pot
disturbances
Figure
the percent
are for the
services
ical Di
real business
s that the ec
technology.
ion of knowle
must
5 in
escot
of te
al fac
ercent
the di
Solo w
progre
uc tuat
ential
s turbance s
cycle
on o my
It is
dge a
uaLLy
ness
short
direct evidence on
He examines
nited States
e percent change in
ed by their factor
the rate of
are
g which
The Evidence on Technolo
of
pticin
ulat
theories have trouble
is subject to such large
a more standard presumpt
nd the concurrent increas
the economy's techno
over time. Yet to m
and
ion
e in
logical opportunities take place grad
imic observed fluctuations, real busi
ub Stanti a 1mai
the
t (Ichno
tor
ntain
produ
986)
logic
produ
that there are sction function.has offered some
al disturbances.ctivity for the U
in Out
inputsI" sho
putare
uld
less th
we ight
measure
change
ffe rent
res idua
ss. Pre
ions in
ly impor
as a source of
1 presents my ca
change in output
private economy
Like Prescott, I
scott points out that there
the Solow residual, a findin
tant role for technological
business cycle fluctuations.
iculation of the Solow residual and
yearly since 1948. (Both variables
less agriculture and housing
find substantial fluctuations in
10
year.
Figure 1.
cyclical. In
productivity a
of the change
recessions are
The Solow
regarding exoge
standard explan
labor hoarding
Productivity ap
also shows
every
lso fe
fn the
perio
res id
nous
ation
and o
pears
r input
earl
that
lid measure
then
2A related explanation of the procyclical behavior of the
Solow residual has recently been proposed by Hall (1987): Hallpoints Out that if price exceeds marginal cost because ofimperfect competition, then the measured Solow residual willappear procyclical even if the true production technology isunchanging. Alternatively, the Solow residual could reflectendogenous changes in technology due to demand shocks: suchendogeneity might arise if, for example, learning-by-doing isimportant.
11
1 factor
tivity fe
measured tota
factor produc
3.4 percent.
the economy'
aggregate pr
productivity. For
11 by 3.5 percent,
example,
while in
in 1982
1984 it
total
rose by
One might interpret these numbers as showing
s ability to convert inputs into outputs--the
oduction function--varies substantially from year
that measured productivity is highly
total factor
to
year in which output fell,11. If the Solow residual is a va
available production technology,
ds of technological regress.
ual need not be interpreted as evidence
technological disturbances, however. The
of cyclical productivity is that it reflects
ther "off the production function" behavior.
to fall in a recession because firms keep
unnece
labore
wi thou
A
ssary andrs begin
t a largen examina
unde
to pu
incr
tion
rutili
t Out
ease jof the
zed labor. In
greater effort;
n measured labo
data from the
a boom the hoarded
output increases
support this standard explanation of
2
y 1940s appears to
the cyclical behavior of
productivity. The increase in output associated with the World
War II build-up
Yet from 1939
average of 7.
productivity
1950.) One m
economic boom
rather than de
that the Solow
of changes in
Once the
year changes
longer any di
disturbances.
fluctuations,
disturbances.
available tech
real business
An advoca
economic model
formal evidenc
plausibility t
disturbances. R
widespread atten
however, no disc
demand-driven
1 factor produc
By contrast, th
since then is 5
inding as showin
fact driven by s
e appealing inter
good measure over
nological abilities.
rejected as a measure of year-to-
the
ump t
phenomenon.
tivity grew
e most
.2 percent
g that the
upply shoc
pretation
short hor
an
n
ks
is
izons
is most plausibly a
944 measured tota
cent per year.
rown in any year
interpret this f
he l940s was in
shocks. A mor
idual is not a
economy's tech
w residual is
e available production technol
evidence for substantial techn
to generate fluctuations that
bu mess cycle models require
ex stence of large fluctuatio
y s a crucial but unjustifie
eory.
to 1
6 per
has g
ight
of t
mand
res
the
Solo
in th
rec t
Yet
real
The
no lo
cyci
te 0
s of
e
0
ogy, there is no
ological
mimic observed
such
ns in
d ass ion of
S
1.
g i
e th
f re
ten
Yet
the as
ecessi
tion from
ussion of
al business
rely on ass
more casual
sumption of
ons are
that
no
cycle theory might respond
umptions for which there is
evidence also does not give
subs tantial technological
events; they receiveimportant
policy-maker
declines in
s and the medi
the available
If society suffered some important
12
a. Th
techno
ere is,
logy.
adverse technological shock,
we would be aware of it. My own reading of the newspaper,
Whether changes in energy prices affect the Solow residualcomputed from GNP depends on a variety of issues involving theconstruction of index numbers like CNP. See Bruno and Sachs(1985, P. 43) for a discussion.
4Hamilton (1983) finds oil price changes are also associatedwith the pre-OPEC recessions. Yet these prices changes are muchtoo small to explain plausibly such large declines inproductivity.
13
however, does not lead
exogenous deteriorati
The OPEC
when the econo
easily identif
that the econo
1974 and 1979,
recessions in
Solow residual
changes in the
find events wi
ene
my
i ab
my
as
the
S.
ag
th
me to associate most recessions with some
on in the economy's productive capabilities.
price changes of the l970s illustrate that
riences large real shocks, these shocks are
nd much discussed. Figure 1 indeed shows
rienced large negative Solow residuals in
might have expected.3 Yet the five other
t-war period also exhibit large negative
explain these Solow residuals as adverse
r gy
expe
le a
exp e
one
pos
To
gre
the
gate production
economic signi
The apparent absence of
function, one
ficance of the
such events is
recessions cannot be easily attributed to
would need to
OPEC price
evidence thatincreases
these
4shocks
Labor Suoolv and Intertemooral
Real business cycle theori
employment are fully voluntary.
economy always finds itself on
the typical business cycle, emp
exogenous real
Substitution
sts assume that fluctuations in
In other words, they assume the
the labor supply curve. Yet over
loyment varies substantially while
pattern, rea
very willing
significanti
response to
response to
It is u
to interternp
supply typic
substitute 1
inter tempo r a
assume, then
wage should
Individuals
work hard to
individual 1
the real
(Altonj i
time.
1 business cyci
to reallocate
y reduce the qu
small temporary
small decreases
nlikely, howeve
oral relative p
ally finds that
eisure over tim
lly
in
wor
fac
day
ab or
upply - -
ightly.e model
leisure
anti ty
reduc t
in the
r, that
rices.
the w
e is s
and the real
s observed
individuals
Individuals
ey supply in
real wage or in
metric
ess of
If lei
us mes s
increa
n the future.
their real wage
future. Yet studies of
Personal experience
to judge the behavioral re
models rely. One key beh
labor supplied reacts subs
Jithout such intertemporal
and introspec
sponses on wh
avioral respo
tantially to
substitution
14
tion provide ano
ich real busines
nse is that quan
the real interes
real business
ther way
s cycle
tity of
t rate.
cycle
the determinants of labor s
interest rate- -vary only sl
the real wage
To mimic thi
s require that
over time.
of 1ãboTth
ions in the
be
must
real interes
individuals
t rateare so
evidenc
individ
sure we
cycle
ses in
responsive
e on labor
uals to
re highly
theorists
their real
substitutable, as
dividuals facing e
k little today and
ing expected decre
and enjoy leisure
supply over time
Econo
ill ingn
light.
real
xp e C te
much
ases i
in th
find
change
duals
b
d
i
n
e
t
5
do
lo
wage
1985
should
lead
Ball
to only
1985)
small
Indivi
real wage changes by substantially real
hat expe
in hour
not re
cating
cted changes in
s worked.
spond to expected
leisure over
models are unable to explain how a temporary increase in
output
em pla
t cons
0 acce
laymen
ends on
at labo
ation I
i tutab i
and employment.
usible. The real
ideration when md
Pt new employment.
and students that
the price of app
r supply depends
draw from this o
lity of leisure i
Yet
imte
ivid
Jh
the
les, it is
on the
bservation
s very
government purchases increases
behavioral response does not se
rate is simply not a significan
decide to leave their jobs or t
economists can easily convince
quantity of apples demanded dep
much harder to convince them th
real interest rate. The implic
is that the intertemporal subst
such a
rest
ual s
ile
likely- far too weak to get real business cycle models
Cycle Th
bus imes s
duct ion
eories
cycle
with Mul
theories
to work
cussing so
tiole Se
I have
c tots
been dis
Real Business
The real
far treat pro
This abstractio
business cycle
Some real
technologies of
changes in techn
highlight the in
to the different
as if it takes place in a single industry.
is not characteristicn, however,
theories
business cycle the
different sectors
ology. (Long and
teractions among
sectors are inde
of all real
ze changes in
economy-wide
These model
Even if the
outputs of th
an adverse s
ones emphasi
rather than
Plosser 1983)
the sectors.
pendent, the
For example,different
to one 5
economy;
sectors move together.
ector reduces the
these individual
the
5
shocks
e
hock
for
wealth of the individuals in the
s respond by reducing their demand
15
all goods. An observer would see an aggregate business cycle,
even without a single aggregate shock.
To get these real business cycle models to work, however,
the number of independent sectoral shocks cannot be too great.
If there were many independent sectoral shocks and labor were
mobile between sectors, then the law of large numbers would
guarantee that these shocks and their effect on the aggregate
economy would average out to zero. To get an aggregate business
cycle, these models therefore require that there be only a few
sectors and that these sectors be subject to large technological
disturbances. These models are therefore similar to the single-
sector theories and suffer from the same weaknesses: the absence
of any direct evidence for such large technological disturbances
and the implausibility of strong intertemporal substitutability
of leisure.
A second type of sectoral shock theory emphasizes the costly
adjustment of labor among sectors. (Lilien 1982) These models,
which depart more from the Walrasian paradigm, assume that when a
worker moves from one sector to another, a period of unemployment
is required, perhaps for job search. In this case, independent
shocks across many sectors do not offset each other. Recessions
are, according to these theories, periods of more sectoral shocks
and thus greater intersectoral. adjustment.
This type of real business cycle theory may appear more
plausible than those relying on substantial aggregate
productivity shocks and intertemporal substitution. It is
16
Money and Prices over the Business Cycle
Before real business cycle theory
debate in the early 1980s, almost all
agree on one conclusion: money matters.
discussions of business cycles (Friedman
more formal econometric work (Barro 1977)
Reserve as an important source of macroeconomic disturbances.
While there was controversy as to whether systematic monetary
policy could stabilize the economy, it was universally accepted
that bad monetary policy could be destabilizing.
17
perhaps easier to imagine that recessions are characterized b
unusually great need for intersectoral reallocation than by s
sort of major technological regress that makes leisure unusua
attractive. Yet the available evidence appears not to suppor
this intersectoral story. If workers were unemployed volunta
y an
ome
1 ly
t
r i ly
in recess
sectors
with high
opposite
levels of
Moreover,
measured
procyclic
theory is
economic
ions because
we would expe
job vacancy.
pattern: high
help wanted
in contrast
mobility of w
al. (Murphy
also unable
fluctuations
they were moving to new jobs in other
Ct to find high unemployment coinciding
Yet observed fluctuations have just the
unemployment rates coincide with low
advertising. (Abraham and Katz 1986)
to the prediction of this theory, the
orkers between sectors is strongly
and Topel 1987) This real business cycle
to be plausibly reconciled with observed
nomic
d to
entered the macroeco
macroeconomists seeme
Both historical
and Schwartz 1963)
pointed to the Fe
and
deral
it is ironic that real business cycle theory arose in the
wake of Paul Voicker's disinflation. Many economists view this
recent experience as clear confirmation of -the potency of
monetary policy. Voicker announced he was going to slow the rate
of money growth to achieve a lower rate of inflation; the rate of
money growth in fact slowed down; and one of the deepest post-war
recessions followed, as did an eventual reduction in the rate of
inflation. This set of events is easy to explain within the
context of Keynesian theory with its emphasis on the gradual
adjustment of wages and prices. It is less easy to explain
within the context of real business cycle theory.5
Robert King and Charles Plosset (1984) explain the
historical association between money and output by arguing that
the money supply endogenously responds to fluctuations in output.
Standard measures of the money supply such as Ml are mostly
inside money, that is, money created by the banking system. King
and Plosser suggest that the transactions services of inside
money should be viewed as simply the "output" of one sector of
the economy, the banking sector. Just as one should expect the
outputs of different sectors to move together within a multi-
sector real business cycle model, one should expect the output of
the banking sector to move with the outputs of other sectors. An
increase in productivity in any sector will tend to increase the
The recent disinflation is not unusual. Romer and Romer(1989) show that output typically falls after the Fed makes anexplicit decision to reduce inflation, which they interpret asevidence against real business cycle theory.
18
While the story of K
procyclical behavior of money,
behavior of prices. It is a
absence of identifiable real
changes, inflation tends to r
This famous Phillips curve co
the macroeconomic debate of t
empirical motivation for the
1970s. (Friedman 1968, Lucas
and Plosser generates procycli
transactions services, these f
associated with fluctuations i
fluctuations in prices. The
been left without an explanat
theorists6
it cannot explain the pro
documented fact that,
s such as the OPEC oil
n booms and fall in re
tion played a central
60s, and it was the pr
new classica
Yet since
money through the demand
luctuations in money will be
n real balances not with
short-run Phillips curve
ion by real business cycle
6Indeed, as King and Plosser point out, their model makes
the counterfactual prediction that the price level should becountercyclical: since the demand for real outside money probablyrises in a boom, and it is the outside money stock that pins downthe price level, equilibrium in the market for outside moneyrequires that the price level fall in a boom.
19
demand for transactions services; the banking system responds by
creating more inside money. Hence, the procyclical behavior of
standard monetary aggregates cannot necessarily be interpreted as
evidence that changes in outside money caused by the monetary
authority have real effects.
ing and Plosser can explain the
wel
sho
ise
rre
he
ea
1
1
I-
La
19
ny972
cal
cyclical
in the
price
ce S S ions
role in
ima ry
1 theories
the model o
in the
f King
for
has thus
The Tradeoff between Internal, and External Consistency
A good theory has two characteristics: internal consistency
and external consistency. An internally consistent theory is one
that is parsimonious; it invokes no ad hoc or peculiar axioms.
An externally consistent theory is one that fits the facts; it
makes empirically refutable predictions that are not refuted.
All scientists, including economists, strive for theories that
are both internally and externally consistent. Yet like all
optimizing agents, scientists face tradeoffs. One theory may be
more "beautiful," while another may be easier to reconcile with
observation.
The choice between alternative theories of the business
cycle--in particular, between real business cycle theory and new
Keynesian theory- - is partly a choice between internal and
external consistency. Real business cycle theory extends the
Wairasian paradigm, the most widely understood and taught model
in economics, and provides a unified explanation for economic
growth and economic fluctuations. New Keynesian theory, in its
attempt to mimic the world more accurately, relies on nominal
rigidities that are observed but only little understood. Indeed,
new Keynesians sometimes suggest that to understand the business
cycle, it may be necessary to reject the axiom of rational,
optimizing individuals, an act which for economists would be the
ultimate abandonment of internal consistency.
The tension between these two goals of science will
undoubtedly continue. Each school of macroeconomic thought will
20
highlight its strengths while trying to improve on its
weaknesses. My own forecast is that real business cycle
advocates will not manage to produce convincing evidence that
there are substantial shocks to technology and that leisure is
highly substitutable over time. Without such evidence, their
theories will be judged as not persuasive. New Keynesians,
however, have made substantial progress in recent years toward
providing rigorous microeconomic foundations, the absence of
which was the fatal flaw of the Keynesian consensus of the l960s.
Jhile real business cycle theory has served the important
function of stimulating and provoking the scientific debate, it
will, I predict, ultimately be discarded as an explanation of
observed fluctuations.
21
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Altonji, Joseph G.,
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23
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