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8/14/2019 Doing Good or Doing Well? Image Motivation
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Doing Good or Doing Well? Image Motivation and
Monetary Incentives in Behaving ProsociallyDan Ariely, Anat Bracha , and Stephan Meier
January 22, 2008
Abstract
This paper experimentally examines image motivationthe desire to be liked andwell-regarded by othersas a driver in prosocial behavior (doing good), and askswhether extrinsic monetary incentives (doing well) have a detrimental effect on proso-cial behavior due to crowding out of image motivation.
By denition, image depends on ones behavior being visible to other people. Usingthis unique property we show that image is indeed an important part of the motivationto behave prosocially. Moreover, we show that extrinsic incentives interact with imagemotivation and are therefore less effective in public than in private. Together, theseresults imply that image motivation is crowded out by monetary incentives; which inturn means that monetary incentives are more likely to be counterproductive for publicprosocial activities than for private ones.
Keywords : prosocial behavior, extrinsic incentives, image motivation, experiments
JEL : D64, C90, H41
Sloan School of Management, Massachusetts Institute of Technology.The Eitan Berglas School of Economics, Tel Aviv University.The Federal Reserve Bank of Boston.
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1 Introduction
Most charitable organizations depend on private contributions, in the form of monetary gifts,
volunteer efforts, or other tangible contributions, such as blood donations. The magnitude
of private contributions is impressivein the United States alone 89 percent of households
donate, averaging $1,620 per year, and 44 percent of US adults volunteer the equivalent of 9
million full-time jobs (Independent Sector, 2001). This prosocial behavior is striking in light
of the economic incentive to free-ride in the provision of public goods. In order to elicit con-
tributions, charitable organizations use many creative efforts to incentivize voluntary giving.
For example, the Lance Armstrong Foundation recently launched the LIVESTRONG cam-
paign where individuals contribute by purchasing colorful wrist bands, many organizations
give thank-you gifts, such as mugs and calendars, and charities organize walks, concerts, and
advertise lists of their donors. In addition, the government helps increase charitable giving
by offering tax breaks for such donations.
The various types of charitable contributions and the many real-life ways of soliciting
such donations suggest that there may be different motives for individuals to behave proso-
cially. These motives are roughly divisible into three broad categories: intrinsic, extrinsic,
and image motivation. Intrinsic motivation is the value of giving per se, represented by
private preferences for others well-being, such as pure altruism or other forms of prosocial
preferences (for surveys, see Fehr and Schmidt, 2003; Meier, 2007). Extrinsic motivation is
any material reward or benet, either monetary or non-monetary, associated with giving,
such as thank-you gestures and tax breaks. Image motivation , or signaling motivation, refers
to individuals tendency to be motivated partly by how others perceive them. Image motiva-
tion therefore captures the rule of opinion in utility, i.e., the desire to be liked and respected
by others and by the self. If individuals are looking for social approval in their behavior,
then they should try to signal traits which are dened as good based on social norms and
values (for economic models incorporating social approval, see e.g., Akerlof, 1980; Hollander,
1990; Benabou and Tirole, 2006; Andreoni and Bernheim, 2007; Ellingsen and Johannesson,
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2007, 2008). Being altruistic is often seen as good, and being greedy or selsh is not.
Prosocial behavior is therefore a way to signal to others that one is good. 1
The desire for social approval implies that, conditional on prosocial activity yielding a
positive image, people will act more generously and prosocially in public than in privatesettings. A number of eld and laboratory studies have found such a pattern (e.g., Andreoni
and Petrie, 2004; Dana et al., 2006; Rege and Telle, 2004; Soetevent, 2005). This may explain
why many organizations make individuals contributions explicitly visible to others by having
charity walks, offering wrist bands, posting lists of donors, etc. Indeed, very few donations
are actually done anonymously (see Glazer and Konrad, 1996).
While these three motivations (intrinsic, extrinsic, and image) have separate effects on
prosocial behavior, they may also interact with each other. Following Titmuss (1970), who
claimed that private monetary incentives for blood donations would decrease blood supply,
a number of empirical studies have shown that private monetary incentives indeed have
negative effects on prosocial behavior (e.g., Frey and Oberholzer-Gee, 1997; Gneezy and
Rustichini, 2000a,b; Mellstroem and Johannesson, 2008). While there are a few studies
showing detrimental effects of extrinsic incentives, less is known about the mechanisms by
which this occurs. A number of explanations have been offered: extrinsic motivations might
interact with the intrinsic motivations in the decision to undertake a task (e.g., Deci, 1975;
Frey, 1997); extrinsic incentives might destroy trust in a principal-agent relationship, leading
the agent to behave less prosocially (e.g., Falk and Kosfeld, 2006; Fehr and List, 2004; Fehr
and Falk, 2002); or the introduction of extrinsic motives might shift individuals decision
frame from a social frame, in which prosocial behavior is more prevalent, to a monetary frame
in which maximization of self-interest becomes more salient (e.g., Gneezy and Rustichini,2000a; Heyman and Ariely, 2004).
This paper experimentally tests another mechanism by which extrinsic incentives can1Behaving prosocially can also be undertaken instrumentally in order to signal ones wealth or status or
in order to get future extrinsic rewards, like a political career or admission to a college (e.g., Glazer andKonrad, 1996; Harbaugh, 1998a,b; Blumkin and Sadka, 2007).
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have detrimental effects on prosocial behavior: extrinsic incentives might interact with image
motivation by diluting the signaling value of prosocial behavior (see, Benabou and Tirole,
2006). Simply put, when observing a prosocial activity, the addition of extrinsic incentives
makes it more difficult to answer the question: Is the individual behaving prosocially to dogood or to do well? This will affect the image gain from prosocial behavior. Think of the
following scenario: an individual is considering buying a new hybrid car. This car is more
expensive than an equivalent car operating with a standard gasoline engine, but the hybrid
car helps in preserving the environment. Driving around a car which is clearly a hybrid car
would probably add to ones positive image, especially if she lives in a community that values
environmentally-friendly technologies. Suppose now that the government gives a large tax
benet for those who decide to purchase a hybrid car (and everybody knows about this).
The tax incentive, of course, reduces the price of hybrid cars and therefore should make
the hybrid car more attractive for the individual. However, the tax incentive also decreases
the image value of driving the hybrid car. Without the tax incentive, buying the hybrid
car denitely shows the individual cares for the environment (positive image), with the tax
incentives, it does not. More generally, when extrinsic incentives are provided (such as a
tax benet), it is difficult to conclude whether the prosocial act is due to ones innate good
traits (the persons concern for the environment) or due to greed (receiving a tax benet).
Therefore, if image indeed motivates prosocial behavior, introducing extrinsic rewards may
reduce image motivation, which can lead to a negative net effect (relative price effect net of
crowding out effect) on prosocial behavior.
To test for image motivation and its interaction with monetary incentives we develop
two behavioral hypotheses. The hypotheses make use of the different properties of thedifferent incentives driving prosocial behavior. Namely, intrinsic and extrinsic motivations
are personalaltruism, as an example of intrinsic motivation, is a personal taste, while
monetary payment and gifts, as examples of extrinsic motivation, are personal material
rewardsyet image motivation is a social motivation that depends on the visibility of ones
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actions. Importantly, the interaction between extrinsic incentives and image motivation
depends on the prevalence of image motivation and therefore on the visibility of the prosocial
behavior. In anonymous prosocial decisions, for instance, extrinsic monetary incentives will
not crowd-out image motivation, as in this setting there is no image motivation to beginwith. 2 If extrinsic motivation does crowd-out image motivation, we expect that extrinsic
incentives will be more effective in private decisions to behave prosocially than in decisions
which are publically visible (Effectiveness Hypothesis). Consequently, extrinsic incentives
are more likely to be counter-productive in public rather than private decision-making.
We conduct an experimental study to investigate whether image considerations indeed
play a part in motivating prosocial behavior, and how this motivation interacts with extrin-
sic monetary rewards. Our test of the interaction between extrinsic and image motivation
uses the unique property of image concerns its dependence on visibility. More specically,
in the main experiment, named Click for Charity, subjects could donate to a charitable
organization by clicking two keys on the keyboard. Participants were randomly assigned to
make their donation choices in a public or in a private setting, and were randomly assigned
to receive, in addition to the donation made on their behalf, monetary incentives that ac-
crued solely to them. In addition, they were randomly assigned to one of two charities (the
American Red Cross or the National Rie Association (NRA)) which were either associated
with positive or negative image consequences. In the main analysis we focus on the good
charity as it is a clear prosocial activity. The good charity is dened either according to the
consensus at Princeton (the Red Cross), or according to participants perception of the ma-
joritys view on campus. The results strongly support the hypotheses that image motivation
is important for prosocial behavior, and that private monetary incentives partially crowd-outimage motivation. That is, without monetary incentives we nd signicantly greater effort
in public than in private; when monetary incentives are introduced, monetary incentives
have no effect on effort in public, while they do increase effort in private, and this differen-2There may be self-image which exists also in anonymous giving. However, here we take image to be the
value added by others opinion, and not of one own opinion.
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tial effect is statistically signicant. The results for a bad cause with a negative image
valuedened either according to the consensus at Princeton (the NRA), or according to
participants perception of the majoritys viewsupport the partial crowding out hypothesis
as well. That is, introducing monetary incentives have no effect on contribution effort inpublic, while monetary incentives do increase the contribution effort when the decision is
private. We were able to further examine some of these hypotheses in a eld study (which is
more limited due to our setup), and in general the results support what we nd in the lab:
private monetary incentives seem to interact negatively with image concern, leading to the
result that monetary incentives are more effective in motivating private prosocial decisions
than ones made in public.
The paper proceeds as follows: Section 2 presents the behavioral hypotheses. Section 3
presents the experimental design, and section 4 the results. Section 5 presents the illustrative
eld study. Section 6 discusses the implications of our ndings and concludes.
2 Behavioral Hypotheses
This section develops behavioral hypotheses for our experimental setting to test for imageas a driver in prosocial behavior and to test whether extrinsic monetary incentives crowd-
out image motivation. An individuals incentives to behave prosocially can be divided into
three basic motivations: intrinsic, extrinsic, and image motivation. Intrinsic motivation is a
personal taste for giving per se, extrinsic motivation is any personal material reward, either
monetary or not. Image motivation is inuenced by what other people think. There are
many personal traits that yield positive image: being prosocial, fair, or caring; while being
unfair, or greedy, reduces or even yields negative image (e.g. Benabou and Tirole, 2006;
Andreoni and Bernheim, 2007; Ellingsen and Johannesson, 2008).
We focus on the case where individuals image is a function of how prosocial or greedy
other people think she is, as in Benabou and Tirole (2006). 3 The more people think one3In the Appendix we formally present the model of Benabou and Tirole (2006), and show how to derive
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is prosocial, the greater is the image value of her prosocial act. However, the more people
think she is greedy, that is behaving prosocially to receive the extrinsic rewards, the lower
is the image value of her prosocial activity. A crucial property of image is its dependency
on visibility, after all image is a consequence of what others think. So if image value from aprosocial activity is positive, increasing the number of observers, increases the image value
of the prosocial activity and, as a consequence, leads to higher effort.
Even though we mainly focus on an activity with positive image value, following the same
logic increasing visibility should decrease effort for an activity with a negative image value.
This leads to the rst behavioral hypothesis on image-motivation:
Image-Motivation Hypothesis: Ceteris paribus, changing visibility changes the level of prosocial activity. For a positive (negative) image, increasing visibility increases (de-
creases) the level of prosocial activity.
Note that the case of self-image does not affect the Image-Motivation Hypothesis if self-
image is independent of visibility. In the experimental set-up, self-image can be thought of
as a constant in all conditions and does not affect the conclusions.
Introducing extrinsic incentives (or increasing thereof) affects prosocial behavior bothdirectly by increasing the extrinsic rewards, and through image motivation. On the one
hand, the relative price effect will increase prosocial activity, but, on the other hand, higher
personal benets associated with a prosocial activity tends to decrease its image value. The
intuition is that if an individual receives greater extrinsic rewards for the activity, she is a
suspect to behave prosocially for the extrinsic rewards rather than for intrinsic motivation.
Since being thought of as greedy is negative, this reduces the image value of the prosocial
activity. In such a case, offering a greater material reward may backre, depending on which
effect is stronger - higher extrinsic reward or lower image motivation.
Importantly, while the relative price effect is independent of visibility, the potential
crowding-out of image motivation crucially depends on visibility. As a consequence, the
the behavioral hypotheses based on this mode. Evidently, there are other possible setups one could consider.
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effect of extrinsic rewards on image motivation implies that visibility may inuence the
effectiveness of material rewards. That is, if receiving an extrinsic reward reduces image
motivation (positive or negative), then greater publicity amplies this reduction and reduces
the effectiveness of material reward. This leads to our second hypothesis on the effectivenessof monetary incentives:
Effectiveness Hypothesis: Extrinsic rewards are less effective the greater is the visibility
of the prosocial act.
The Effectiveness Hypothesis implies crowding-out of image motivation. This conclusion
is possible even if extrinsic incentives do not have a negative net effect on prosocial activities,
i.e. when the direct increase in utility from extrinsic rewards outweighs any decline in
image motivation. Whenever prosocial activity level increases with monetary rewards it
is normally difficult to conclude whether extrinsic rewards crowd-out image motivation.
However, according to the Effectiveness Hypothesis, extrinsic rewards are less effective with
more visibility only as long as material rewards reduce image motivation. Therefore, the
case of higher prosocial activity with higher monetary rewards in which visibility reduces
the effectiveness of extrinsic rewards implies crowding-out. As a result, a detrimental effect
of extrinsic incentives (a negative net effect) is more likely to occur for a visible prosocial
effort than for a private one.
In the following sections, we test these hypotheses experimentally.
3 Experimental DesignClick for Charity
The experimental design has to fulll three criteria: (1) the prosocial task needs to have
clear image implications by allowing one to signal personal traits, (2) ones decision has to
be made either public or private, and (3) extrinsic monetary incentives have to be either
offered or not and to be publicly known.
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In this study, participants could behave prosocially in a real-effort task: sequentially
pressing two keys X and Z on the keyboard for up to 5 minutes. For every completed
pair of clicks, we donated on the participants behalf to an assigned charity, hence, the name
Click for Charity. The donations were made according to a decreasing payment schedule:1 cent was donated for each of the rst 200 pairs of X-Z presses, 0.5 cents for each of the
next 200 pairs, 0.25 cents for each of the next 200 pairs, . . . , and 0.01 cents for each pair
above 1,200. Although marginally decreasing, the more pairs pressed, that is, the higher the
effort, the greater was the donation to the assigned charity. Before the actual task started,
each participant practiced the task for 30 seconds. 161 Princeton undergraduate students
participated in this study; none knew the nature of the experiment before entering the lab.
This study used a between-subjects 2x2x2 design. The conditions differed according to
the tasks visibility, the compensation scheme, and the nature of the charity, as explained
below.
The visibility of the task was controlled by randomly assigning subjects to make their
effort choice in public or in private. In the private condition, the effort decision was
made anonymously, while in the public condition, the choice was disclosed to others. At
the end of the task, we asked those in the public treatment to tell the other participants in
the lab which charity they were assigned to, whether they also earned money for themselves
(based on the payment scheme below), and how much money they donated to the charity
(and got for themselves).
The payment scheme was such that a random selection of participants could, in addition
to the donation, earn money for themselves. The private payment was exactly the same as
the donation schedule described above.The nature of the cause was manipulated by randomly assigning subjects to one of two
charities: the American Red Cross or the National Rie Association (NRA). Making efforts
to benet one of these charities is expected to have signaling value. Whether the value of
the signal is positive or negative depends at least partially on the norms and values of the
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community and therefore on others (observers) opinions (as a result the two charities might
be perceived differently at Princeton and at a University in a pro-gun state). Therefore, we
classify the assigned charities as good or bad either not taking individual perceptions into
account (and relying on the consensus view) or by controlling for individuals perception of what others identify with. The rst classication analyzes the treatments with the Red Cross
and the NRA separately. According to our survey at Princeton, the majority of students
(i.e. students in the laboratory database) positively identies with the Red Cross (92% of
participants), and negatively identies with the NRA (72% of participants). According to
this consensus on campus, the Red Cross is clearly considered good and the NRA bad.
The second classication is based on the perceived majoritys view (on an 11-point scale
from -5 not at all identify to +5 very much identify) 4: a charity is considered good if
the reported perception is positive and bad if the reported perception is negative. 5 Seven
subjects stated a neutral perceived identication (exactly zero). When creating a dummy
for good or bad charities based on perceived others identication, we focused on the
remaining 154 subjects. However, when we control for perceived others perceptions using
the full scale or when we use the classication based on the consensus, all participants are
included. We will use both classications in the analysis.
The treatment with negative signaling value allows us to both examine how the results
for a good cause translates into a negative domain, and to refute alternative explanations
to the Image-Motivation Hypothesis. That is, one may think individuals put more effort in
public than in private not for the signal value of their actions, but for other reasons such as
showing they are very good in clicking. Such a tendency to show key pressing skills in public
should, of course, not interact with receiving an incentive and is, therefore not alternativeexplanation for the Effectiveness Hypothesis.
4In fact, we asked participants before the study started about the identication of Princeton studentswith a number of charities
5As one anonymous referee noted, false-consensus effect the tendency of people to think others aresimilar to them in views may be present. To minimize this effect, we selected extreme organizations: onethat the majority on campus does identify with, and one that the majority on campus does not identifywith. Hence, by construction the majority perceived the consensus correctly.
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The following section presents the results of the study.
4 Results
We present the results in three steps: rst, we present the analysis for good and bad
causes separately, then we present the analysis for all causes together, and lastly we test
whether a physical limit on the ability to continuously press keys can explain the results.
Figure 1 shows clicking effort in public and in private, with and without private monetary
incentives for a good cause. Panel A shows effort for a good cause, dened according to
the consensus view at Princeton (the Red Cross). Panel B shows effort for a good cause
dened as what participants think others identify with. This classication takes into account
personal perception, while the classication of panel A does not. Comparing the two panels
we nd the same qualitative results.
First, without any private monetary incentives, subjects put forth signicantly more
effort in the public than in the private condition. In the public condition, they pressed, on
average, approximately 900 pairs for the Red Cross (822 pairs for a good charity), while
in the private condition, subjects pressed only about 517 for the Red Cross (548 pairs for agood cause). The difference is statistically signicant in a t-test 6 on the 1 percent level
and 5 percent level, respectively. In line with the Image-Motivation Hypothesis, subjects
exerted more effort for a good cause in public, where they are able to signal their effort to
many others.
[Figure 1 about here]
Second, while monetary incentives do not increase effort in public, they do increase effort
signicantly in the private condition. In the public condition, there is an insignicant decline
in effort from 900 to 814 key pairs on average for the Red Cross (from 822 to 702 key pairs
for a good charity). In the private condition, there is a signicant increase in effort from6We will use t-tests to compare all means, unless otherwise noted.
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517 to 737 key pairs on average for the Red Cross ( p < 0.05) (from 548 to 740 key pairs on
average for a good cause, p < 0.05). Under both classications, the different impact of
incentives in public and in private is statistically signicant on the 5 percent level. 7 As we
show at the end of this section, this result is not driven by subjects in the public conditionreaching a physical limit. Therefore, this result supports the Effectiveness Hypothesis that
private monetary incentives are less effective in public than in private. This implies that
monetary incentives crowd-out the image motivation to behave prosocially.
Panel A and Panel B in Figure 2 show the result for the bad charity, dened according
to the consensus at Princeton (the NRA) or according to the perceptions of the participants,
respectively. For the bad charity case, without incentives, contributions are not signicantly
different in public and private. This result refutes alternative explanations arguing that par-
ticipants press more in public just because they are watched, independent of the image value
of their actions. One example of such explanation is that individuals press more in public to
show that they are good in pressing keys. If this were the case, we would nd signicantly
higher effort in the public sphere also for the bad charity. Although this result is appro-
priate to refute alternative explanations, according to the Image-Motivation Hypothesis we
would expect signicantly lower contributions in public relative to contributions in private
for the bad charity. Although this what we expected, we did not nd it in the data. Given
the low level of contribution for the bad in all conditions, we believe that what we see is
a censoring effet, a minimum level of key-pressing participants do, either because they feel
obliged to fulll their implicit agreement to participate, or because they are bored.
Regarding the Effectiveness Hypothesis, the gure show that monetary incentives increase
effort only in private. In public, monetary incentives slightly increase effort from 336 to 391for the NRA ( p = 0 .66) and slightly decrease effort from 308 to 260 for a bad cause
( p = 0 .76). However, in private, monetary incentives increase effort substantially. For the7The results are robust to focusing on participants who correctly perceived the consensus on campus
and therefore would not have been surprised if we had told them about the consensus at Princeton. SeeFigure A1 in the Appendix.
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NRA, effort increases from 325 to 573 ( p = 0 .10) and for the bad cause from 204 to 559
key pairs ( p < 0.05). While the difference in effectiveness of incentives in private and public
is not statistically signicant for the NRA ( p = 0 .32), it is signicant on the 10 percent level
when classifying a cause as bad according to the perception of the participants ( p = 0 .06).In sum, offering monetary incentives is less effective at increasing effort in public than in
private even for a task with negative image value. As effort for a bad cause is at a very
low level, physical limit cannot explain the differential effect of monetary incentives in the
private and public conditions.
[Figure 2 about here]
Analyzing good and bad causes together, Table 1 shows the difference between private
and public conditions in an OLS regression where the number of key pairs is the dependent
variable. As independent variables, we control for the type of the assigned charity in two
ways: Panel A presents the analysis controlling for whether a participant was assigned to
the Red Cross or the NRA (a good or a bad cause according to the consensus view at
Princeton). Panel B shows the same analysis but controlling for the individual perception
of the majority view (on a full scale: -5 to +5). 8 The results are qualitatively the same in
both panels.
Column (1) in Table 1 shows that, in the private condition, monetary incentives increase
effort signicantly ( p < 0.01). In contrast, column (2) shows that for subjects in the public
sphere, monetary incentives do not increase individual effort. Both panels show that the
nature of the cause is important for peoples effort, but the cause seems to be more important
in public than in private. This is consistent with the view that the signal matters more inpublic than in private. As seen in column (3), the difference in the effectiveness of monetary
incentives in the public versus the private conditions (i.e. the interaction term of private
monetary incentives and the public condition) is substantial and statistically signicant either8The results are robust to controlling for a dummy for good and bad charity based on perceived
identication of others. See table A1 in the Appendix.
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close to the 95 percent level ( p = 0 .059) in Panel A or at the 99 percent level ( p < 0.01) in
Panel B. Also, column (3) shows that the nature of the cause is signicantly more important
in public than in private. The results support both the Image-Motivation Hypothesis, that
the signal matters more in public, and the Effectiveness Hypothesis, that monetary incentivesare less effective in the presence of image motivation, i.e. if an activity with image reward
is public.
[Table 1 about here]
One concern while interpreting the differential effect of monetary incentives in the public
compared to the private condition is that the effect may be due to a physical limit. Subjects
exerting effort for a good cause in the public condition may reach a physical limit even
without incentives. In this case, it might be impossible to increase effort with monetary
incentives, even if subjects wanted to. While the analysis for the bad cause suggests
otherwise, since effort is at a low level in this condition, we nevertheless tested explicitly
whether participants reached a physical limit in the good-cause condition. To nd where
peoples physical limit is, we ran an additional control treatment, the Limit treatment, in
which 26 students from the same subject pool at Princeton participated. In this treatment,participants performed the same key-pressing task for 5 minutes, and their effort decision
remained anonymous. However, in this condition the task was not a donation task; as the
subjects could only earn money for themselves by pressing the keys, and they were paid high
nancial incentives to do so. Subjects got a at rate of 0.11 cents per pair, plus a bonus,
which increased from $2, if they pressed more than 1,000 pairs, to $20, if they pressed more
than 1,500 pairs.
The average number of paired key presses in the Limit treatment was 1,290 (s.e. 44) pairs,
while subjects pressed only 857 (s.e. 61) key pairs for the Red Cross in the public sphere. The
difference between the key presses in the two conditions is statistically signicant ( p < 0.01).
Analyzing the distribution of key pairs for the Red Cross in public and in the Limit treatment,
we nd that while in the Limit treatment nobody pressed less than 900 pairs, 50 percent
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of the participants did so for the Red Cross (see Figure A2 in the Appendix). Therefore,
the ineffectiveness of monetary incentives in the public condition cannot be attributed to a
physical limit, as most subjects could have increased their effort substantially.
5 Field StudyBike for Charity
The Click for Charity results support the view that extrinsic incentives may have detrimental
effects by crowding-out image motivation. This depends on the extent of public exposure
of the prosocial activity, which, in turn, has important implications for the use of extrinsic
incentives in facilitating contributions to public goods. To strengthen the policy implications
of these results, below we present a rst-pass illustration of the results in the eld.
To illustrate whether the effect found in the Click for Charity experiment also translates
to a eld setting, we launched a similarly-designed campaign at the MIT gym, titled Bike
for Charity. In the Bike for Charity campaign, participants could donate to a good or
bad charity by cycling on stationary bikes for up to 10 minutes, at a donation rate of $1
per mile. As in Click for Charity we implemented a between-subject 2x2x2 design. The
visibility was manipulated by randomly assigning subjects to bike in the public view (on thesecond oor of the gym, where everyone works out) or in a private location (the third oor
of the gym, in a private room). The participants were also assigned to receive either private
monetary rewards for themselves or not. Subjects who participated in the rst few weeks of
the campaign did not receive any private monetary incentives, while those who participated
in the last weeks of the campaign, did. The cause of the charity was randomly manipulated
as in Click for Charity. 9
Due to the lack of a randomized compensation scheme, and to the fact that participants
knew in advance that they would be randomly assigned to bike for either a good or a9In the Bike for Charity we used four controversial charities: Two of the four focus on gun control and
are either pro or against stronger gun control (the National Rie Association (NRA) and the EducationalFund to Stop Gun Violence), the other two charities focus on abortion and lobby either for or against it (thePro-Life Association and the Pro-Choice Action League).
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bad charity, selection bias is a concern. More specically, we expect that individuals
whose image is affected the most by monetary incentives will avoid conditions with private
monetary incentives. This, in turn, could dampen the interaction between extrinsic incentives
and image concerns. Similarly, if the nature of the cause is unclear (the most extreme caseis random assignment, as in our study), the more image-concerned a person is, the less likely
she would be to participate in such a campaignto avoid the chance of being associated with
a bad cause. Both selection biases act against the image and the crowding-out hypotheses.
Despite the limits of the Bike for Charity design, the results present suggestive eld ev-
idence for the Effectiveness Hypothesis. 151 participants were assigned to bike either for
a good or a bad charity, where good and bad charities are dened according to
whether participants perceive MIT students identication as positive or negative, respec-
tively. For these participants, adding private incentives is, on average, more effective in
private than in public. Table 2 shows this effect in an OLS regression with distance biked
in miles as the dependent variable. We use the same independent variables as in Click for
Charity, plus a variable for the participants gender. Table 2 shows that extrinsic incentives
increases effort in the private condition (Column 1; p < 0.01) but not in the public condition
(Column 2; p = 0 .96), and as can be seen in column 3 this difference is statistically signicant
( p = 0 .057).10
[Table 2 about here]
The effect obtained in the eld is not as strong as in the lab. However, as discussed, the
lab results are obtained in a fully randomized setting where participants could not self-select
into a condition based on its characteristics (a good/bad cause, and with/without privatemonetary incentives), while in the eld they partly could. Therefore, the suggestive evidence
is encouragingin spite of the selection bias we observe differential effects of monetary10 Adding individuals to the analysis who believe that the charities are seen by other students as neither
positive nor negative and therefore stated a 0 on scale from -5 not at all identify to +5 very muchidentify, as in Click for Charity, does not change the results qualitatively but increases the standard errorsof the estimations.
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incentives between the public and the private conditions. Future research should further
investigate the interaction between extrinsic incentives and image motivation in the eld.
6 Conclusions
The results of the laboratory experiment, illustrated also in a eld study, support our hy-
pothesis that monetary incentives depend crucially on visibility: monetary incentives are
more effective in facilitating private, rather than public, prosocial activity. People want to
be seen as doing good ; without extrinsic incentives, an observer will attribute the prosocial
act to ones good trait which motivates people to behave prosocially. But with extrinsic
incentives, the signal of a prosocial act gets diluted as one might behave prosocially mainly
to do well . The image value decreases, and the incentive becomes less effective. If no one
is watching (i.e. the prosocial decision is private) the incentive to be doing well cannot
dilute any signal to others, and consequently extrinsic incentives are very likely to increase
prosocial behavior.
Our results have important policy implications; for example, if a government considers a
tax benet policy to facilitate the adoption of a new environmentally friendly technology, itshould expect the policy to be more successful for a non-visible technology, such as environ-
mentally friendly water boilers, relative to a visible technology, such as hybrid cars. This is
because hybrid cars, most of which are clearly visible, may partly be purchased as a signal-
ing medium, while water boilers probably are not. By giving tax benets, the government
might unintentionally damage the signaling value vested in hybrid cars. The net effect of the
incentive depends on the strength of the price effect compared with the crowding-out effect.
It is important to note that image crowding-out by monetary incentives is shown here
when both the prosocial decision and the extrinsic incentives are public. If extrinsic incentives
exist but are not publicly known, others opinion should be the same as if no extrinsic rewards
existed. Consequently, major donors to cultural organizations might not want to make their
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extrinsic incentives (e.g. favorable seats) public, as it would dilute the image signal of
their contribution. If decision-makers, such as fund-raisers or policy makers, anticipate the
Effectiveness and Crowding-Out Hypotheses, they should use fewer public extrinsic incentives
for visible prosocial activities. This brings us back to Titmuss and his intuition that monetaryincentives might reduce pro-social behavior. The research in this paper contributes to the
discussion in showing that Titmusss claim crucially depends on the visibility of the prosocial
decision. Therefore if blood donations are sufficiently public, there is good reason to doubt
the effect of extrinsic incentives and even to expect detrimental effect of monetary incentives.
In this study we show empirically that image motivation and visibility are important
for prosocial behavior. However, there are several open questions which this study did not
answer and are left for future research. One is how the conclusion of this research translates
to other circumstances. In particular, there are societies where volunteering may not be
perceived as honorable as in the US. In these cases image might not be a signicant drive in
behaving prosocially. This leads to the second point: how is image motivation constructed?
Norms, perception and personal views are clearly its ingeredients, but we dont know the
mechanism by which image is formed. In this study we overcome this issue by selecting
extreme charities where norms perceptions and personal views are aligned. However, it
would be interesting to understand what would happen in cases where private views may
not be alligned with others views or when the majority view is not clear. Last, but not least:
does crowding-out of image motivation depend on the type of the extrinsic incentive used?
In this study we explore the effect of monetary incentives, which may be different from the
effect of non-monetary incentives. To continue with the hybrid car example, the incentive of
using the carpool lane may not dilute the signal as much as monetary incentives would.
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Figure 1: Effect of Incentives on Prosocial Behavior
Panel A: Red Cross Panel B: GoodCause
0
200
400
600
800
1000
1200
Wi thout Incentive With Inc enti ve
Payment Scheme
N o
. o
f K
e y p r e s s
Private Public
0
200
400
600
800
1000
1200
Without Incentive With Incentive
Payment Scheme
N o
. o
f K
e y p r e s s
Private Public
Note : Error bars are standard errors of the mean. Panel A shows effort for the Red Cross (the majorityat Princeton positively identies with this charity). Panel B shows effort for a good cause according toparticipants perception of others identication at Princeton.
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Figure 2: Effect of Incentives on Effort for a Bad Cause
Panel A: NRA Panel B: BadCause
0
200
400
600
800
1000
1200
Witho ut Incentive Wi th Incentive
Payment Scheme
N o
. o
f K
e y p r e s s
Private Public
0
200
400
600
800
1000
1200
Wi thout Incentive With Inc enti ve
Payment Scheme
N o
. o
f K
e y p r e s s
Private Public
Note : Error bars are standard errors of the mean. Panel A shows effort for the NRA (the majority at Princetondoes not identies with this charity). Panel B shows effort for a bad cause according to participants perceptionof others identication at Princeton.
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Table 1: Effect of Private Incentives in Click for Charity
(1) (2) (3)Private Public All
Panel A: Controlling for Red Cross and NRAPrivate monetary incentive (=1) 231.95 0.64 231.95
(2.82)*** (0.01) (2.81)***Public sphere (=1) 26.94
(0.25)Private incentive*Public -231.31
(-1.91)*Nature of cause (RC=1) 179.34 498.02 179.34
(2.08)** (5.69)*** (2.08)**Nature of Cause*Public 318.68(2.59)***
Constant 332.05 358.99 332.05(4.27)*** (4.78)*** (4.27)***
N 82 79 161R squared 0.15 0.28 0.22
Panel B: Controlling for perceived identication of othersPrivate monetary incentive (=1) 240.80 -88.88 240.80
(3.01)*** (-0.95) (3.01)***
Public sphere (=1) 152.45(1.80)*
Private incentive*Public -329.67(-2.68)***
Perceived Identication of others 43.55 89.35 43.55(3.00)*** (5.52)*** (3.00)**
Perceived Identication*Public 45.80(2.11)**
Constant 384.43 536.88 384.43(7.11)*** (8.25)*** (7.11)***
N 82 79 161R squared 0.20 0.29 0.25
Note : Dependent variable: Number of key pairs. OLS regressions. t -values inparenthesis. Robust standard errors.Level of signicance : * p < 0.1, ** p < 0.05, *** p < 0.01
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Table 2: Effect of Private Incentives in Bike for Charity
(1) (2) (3)Private Public All
Private monetary incentive (=1) 0.56 -0.02 0.56
(2.78)*** (-0.07) (2.81)***Public sphere (=1) 0.28(1.34)
Private incentive*Public -0.58(-1.93)*
Good cause (=1) 0.84 0.84 0.85(3.75)*** (3.21)*** (4.84)***
Female (=1) -0.54 -0.46 -0.50(-2.71)*** (-2.08)** (-3.30)***
Constant 1.50 1.75 1.48(6.27)*** (6.04)*** (7.30)***
N 69 82 151R squared 0.33 0.18 0.24
Note : Dependent variable: Distance in miles. OLS regressions. t -values inparenthesis. Robust standard errors. Charity classied according to participantsperception of whether MIT students identify with charity (Good if othersidentication is greater than zero and Bad if others identication is lowerthat zero on a scale from -5 not at all identify to +5 very much identify).Level of signicance : * p < 0.1, ** p < 0.05, *** p < 0.01
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A Appendix (Web Appendix)
A.1 Hypothesis Derived from Benabou and Tirole (2006)In Benabou and Tirole (2006) an individuals incentives to behave prosocially are divided
into three basic motivations: intrinsic ( va ), extrinsic ( yvy ), and image motivation R(a, y).Formally, an agents utility is:
U (a) = ( va + yvy )a + R(a, y) C (a),
where a is the extent to which the agent behaves prosocially, y is the extrinsic or monetaryrewards (valued at vy )11 , and C (a) is the cost of behaving prosocially. ( va , vy ) are assumedto be normally distributed, C (a) = ka
2
2 , and R(a, y) is dened as:
R(a, y) = x[ a E (va |a, y) y E (vy |a, y)].
Here, x is the visibility of action a, a is the agents level of concern for being consideredan altruistic or prosocial human-being, E (va |a, y ), and y is the agents level of concern for
being perceived as greedy, E (vy |a, y).
In the analysis leading to the behavioral hypotheses we focus on the case where types
v (va , vy) are distributed normally in the population ( va , vy ) N vavy
, 2a ay
ay 2y,
va , vy > 0, and individuals are assumed to have constant image attitudes ( a , y)
(x a , x y) = ( a , y). Under these assumptions, the optimal level of a is given by Proposition
1 in BT:
Proposition 1 (BT1) Let all agents have the same image concern (a , y ), and cost func-tion c(a) = ka 2/ 2. There is a unique (differentiable-reputation) equilibrium, in which an agent with preferences (va , vy) contributes at the level
a=va + vyy
k+ a (y) y (y),
=va + vyy
k+ xr (y)
where (y) 2a + y ay
2a +2 y ay + y2 2y
and y (y) 1 (y). The reputational returns are E (va |a ,y )
a =
(y)k and E (vy |a ,y )
a = (y)k, resulting in a net value kxr (y) = k(a (y) y (y)), or r (y) = R (a,y )a |x =1 ,independent of a.
11 y represents personal extrinsic rewards only. It does not capture resources available to a charity ororganization which benets from ones prosocial action a . If the individual cares for the total resources forthe organization, this may be incorporated into the intrinsic motivation, va .
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Proof. The proof of this proposition is omitted and can be found in BT.
The aggregate supply, a, is:
a =va + vy y
k+ xr (y),
where (va , vy ) are the populations averages, and xr (y) is the constant (marginal) image
motivation 12 .
A straight-forward conclusion is the Image-Motivation Hypothesis, next:
Proposition 2 a (y)x > 0 r (y) > 0.
The image motivation hypothesis is stated below:
Image-Motivation Hypothesis: Ceteris paribus, changing visibility x changes prosocial
activity a. For a positive image (r (y) > 0), increasing x increases a. For a negative
image (r (y) < 0), increasing x decreases a.
Further calculation leads to the following proposition:
Proposition 3 Let ay = 0 and dene y a . If r (y) > 0,a (y)
x < 0.
Proof. The change in prosocial behavior as we change the extrinsic reward y is given by:
a (y) =vyk
+ a (y) y (y).
a (y)x
= a (y) y (y)
(y) =2a + yay
2a + 2 yay + y22y=
2a2a + y22y
if ay = 0 (y) = 2 (y)(y)
(y) =y2y + ay
2a + 2 yay + y
2
2y
=y2y
2a + y
2
2y
if ay = 0 (y) =2y
2a + y
2
2y
((y) y (y))
a (y)x
= a (y) y (y)
= (y) a (y) y (y) a (y)(y) y (y)(y)
y12 r (y ) = R (a,y )a |x =1 , independent of a.
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If r (y) > 0, i.e., a (y) y (y) > 0,a (y)
x < 0
Proposition 3 implies that, provided a positive net image when x = 1 (private) , the
greater the publicity of ones actions, the less effective are the extrinsic rewards associated
with giving. Note that a (y)x < 0 r (y) = a (y) y (y) < 0. This leads us to the
Effectiveness Hypothesis, and its implication for crowding-out, stated and explained below:
Effectiveness Hypothesis: Extrinsic rewards, y, are less effective the greater is the visi-
bility of the prosocial act, x.
The Effectiveness Hypothesis implies crowding-out of image motivation, r (y) < 013 . Thisconclusion is possible even if extrinsic incentives do not backre, i.e., a (y) > 0. This occurswhenever the direct increase in utility from extrinsic rewards outweighs any decline in imagemotivation . As a result, we have three possible cases:
1. a (y) 0 : this clearly indicates crowding-out
2. a (y) > 0, and r (y) < 0 : crowding-out of image motivation
3. a (y) > 0, and r (y) 0 : there is no crowding-out.
Whenever a (y) > 0, it is difficult to conclude whether extrinsic rewards crowd-out image
motivation. However, according to the Effectiveness Hypothesis, extrinsic rewards are lesseffective with more visibility only as long as material rewards reduce image motivation.
Therefore, the case of a (y) > 0 in which visibility reduces the effectiveness of extrinsic
rewards implies crowding-out. As a result, a detrimental effect of extrinsic incentives is more
likely to occur for a visible prosocial effort than for a private one.
A.1.1 Robustness to other specications
The hypotheses above are for the simple case of no correlation between altruistic taste andpersonal value of extrinsic rewards ( ay = 0) . However, this does not affect our hypotheses.The Image-Motivation Hypothesis says that if image motivation is indeed one of the driversof prosocial behavior and it is positive for some visibility level, then increasing the visibility
13 This also holds for the case of heterogenous image concerns provided that the direct effect of visibilityon the effectiveness of monetary rewards, r (y ), dominates the indirect effect of visibility via image variance(one may suspect prosocial behavior for image concerns).
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of ones actions will increase the level of prosocial behavior a. This hypothesis holds equallywell even if ay = 0 . To see this, note that the image motivation, r (y), is inuenced by ay :
r (y) = a (y) y (y)
= a (2a + yay ) y(ay + y2y )
(2a + 2 yay + y22y )
However if r (y) is positive, increasing the visibility of ones action by x > 1 acts only as an
amplier: xr (y).Similarly, the claim made in the Effectiveness Hypothesis is valid provided that ay is
not too large. To see this, lets examine the following object:
a (y)x
= ax
(y) yx
(y).
Since (y) and (y) are functions of ay , relaxing the assumption that ay = 0 does inuence
the Effectiveness Hypothesis. However, it can be shown that, as long as ay is not too large,
the conclusion still holds.Proof.
(y) =2a + yay
2a + 2 yay + y22y (y) =
2a ay 22a y2y y22y ay2a + 2 yay + y22y
2
(y) =y2y + ay
2a + 2 yay + y22y (y) =
2y 2a y24y 22ay 2y2y ay2a + 2 yay + y22y
2
a (y)x
= a (y) y (y)
= a 2a ay 22a y2y y22y ay
2a + 2 yay + y22y2 y
2y 2a y24y 22ay 2y2y ay2a + 2 yay + y22y
2
If ay = 0 :
a (y)
x=
2ay (2 y) + ay 2 yy2y a 2a a y22y 2 a 2a y2y y 2y 2a y24y
[2a + 2 yay + y
2
2y ]
2
a (y)
x< 0
(2 y )2ay + ay (2y y 2y a 2a a y22y ) a 2y2a 2y y [2a 2y y24y ] < 0
(2 y )2ay + ay (2y y 2y a 2a a y22y ) a 2y2a 2y y[2a 2y y24y ] = 0
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(A)x2 + x(B) (C ) = 0 .
For ay = 0 a (y)x < 0; this implies that there is a solution to the above quadratic equation
in ay (C < 0 B 2 4AC > B 2 > 0). Therefore, as long as ay is small enough, a (y)x < 0.
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A.2 Appendix Figures
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Figure A1: Effect of Incentives for Red Cross and NRA: Restricted to Participants whoCorrectly Perceive Majority Identication
Panel A: Red Cross Panel B: NRA
0
200
400
600
800
1000
1200
Wi thout Incenti ve With Incentive
Payment Scheme
N o
. o
f K
e y p r e s s
Private Public
0
200
400
600
800
1000
1200
Witho ut Incentive With Incentive
Payment Scheme
N o
. o
f K
e y p r e s s
Private Public
Note : Error bars are standard errors of the mean. Panel A shows effort for the Red Cross and Panel B for theNRA (the majority view at Princeton) for individuals who correctly perceive the majority view.
Figure A2: Cumulative Distribution of No. of Key Pairs
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
No. of Key pairs / 100
C u m
u l a t i v e
D i s t r i b u
t i o n
Click for Red Cross Limit' treatment
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Table A1: Effect of Private Incentives in Click for Charity
(1) (2) (3)Private Public All
Panel APrivate monetary incentive (=1) 252.97 -90.81 252.97
(3.01)*** (-0.98) (3.01)***Public sphere (=1) 72.89
(0.64)Private incentive*Public -343.78
(-2.75)***Good cause (=1) 269.68 483.51 269.68
(3.00)*** (5.08)*** (3.00)***Nature of Cause*Public 213.82
(1.63)
Constant 249.29 322.18 249.29(3.29)*** (3.82)*** (3.29)***N 77 77 154R squared 0.21 0.25 0.24
Panel BPrivate monetary incentive (=1) 239.03 -88.52 239.03
(2.93)*** (-0.97) (2.93)***Public sphere (=1) 15.36
(0.14)Private incentive*Public -327.56
(-2.68)***Good Cause 216.19 486.74 216.19
(2.51)** (5.24)*** (2.51)**Good Cause*Public 270.55
(2.13)**Constant 302.29 317.65 302.29
(3.99)*** (4.02)*** (3.98)***N 82 79 161R squared 0.17 0.26 0.22
Note : Dependent variable: Number of key pairs. OLS regressions. t -values in
parenthesis. Robust standard errors. Charity classied according to partici-pants perception of whether Princeton students identify with charity (Goodif others identication is greater than zero and Bad if others identication islower that zero on a scale from -5 not at all identify to +5 very much iden-tify). Panel A: Those stating 0 are excluded from the analysis. Panel B: Forthose stating 0, the assigned charity got classied according to the perceptionof the majority: NRA is perceived as a bad cause and Red Cross as a goodcause.Level of signicance : * p < 0.1, ** p < 0.05, *** p < 0.01