The Tide Rises, the Tide Falls By, Henry Haswarth Longfellow Found by, Grace Brzykcy.
Rises and Falls of Cooperation - Coocan
Transcript of Rises and Falls of Cooperation - Coocan
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Rises and Falls of Cooperation ïŒMacro Analyses of a Social Dilemma Experiment with
Intergroup MobilityïŒ
Jun Kobayashi, Yuhsuke Koyama, Hideki Fujiyama, and Hirokuni Oura (University of Chicago) (Tokyo Institute of Technology) (Dokkyo University) (Teikyo University)
Abstract: We report cyclic rises and falls of the group cooperation rate in a social dilemma experiment with intergroup
mobility. How do the group cooperation rate and the group size affect each other? Olson argues negative
effects of the group size on cooperative behavior. Yet the counter effect of cooperation on the group size is yet
to be fully examined. For this purpose, we conduct a social dilemma experiment with intergroup mobility (with
170 participants in ten sessions). We analyze data at the macro group level. (i) We observe the positive effect
of the group cooperation rate on the group size. (ii) This leads to the cyclic rises and falls of the group
cooperation rate. (iii) Intergroup mobility accelerates the cycle.
Keyword: Cooperation, free-rider, social dilemmas, mobility, experiment
1. Introduction
1.1 Cooperation and Group Size
Olson (1955) theoretically argues that as the group size increases, we can expect fewer participants.
This negative effect of the group size on cooperation has been empirically supported, both in
laboratory experiments and field surveys (Kollock 1998).
Such situation has been conceptualized as âthe free-rider problem.â It occurs in groups or even
in structured organizations, such as shirking in workplaces, not donating, tax evasion, and
environmental pollution. Those people are called âfree-riders.â
However, the counter effect of cooperation on the group size is yet to be fully investigated. If
we leave it unsolved, we may fail to understand the causal mechanism of the free-rider problem.
Ehrhart and Keser (1999) is the only exception. Still, they controlled no condition, so we cannot
estimate the exact effect. Therefore, we investigate the following research question.
Research question. How the group cooperation rate and the group size affect each other in social
dilemmas? Especially how does the group cooperation affect the group size when mobility costs
vary?
We extend Ehrhart and Keserâs experimental design by adding various mobility costs. We
conduct a laboratory experiment because our research question requires well-manipulated design,
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which cannot be expected in field surveys.
1.2 Literature
The free-rider problem is generalized to âsocial dilemmas.â Social dilemmas depict conflict between
individual rationality and collective efficiency. In a social dilemma, rational persons would free-ride
on othersâ contributions rather than contribute. Yet if many people free-ride, serious dissonance will
result.
Dawes (1980) gave a formal definition of social dilemmas. In a social dilemma, persons have
options of âcooperationâ (voluntary contribution to the group) and âdefectionâ (noncontribution).
1. Defection always provides higher payoff than cooperates.
2. But if everyone defects, they receive less payoff than if everyone cooperates.
Payoff is measured in an objective, material scale.
In the literature, social dilemmas have been studied mostly without mobility. However, as
Hirschman (1970) correctly points out, we often have options to âexitâ from a group in the real world.
This holds true especially in modern societies.
Tiebout (1956) predicted that if people are fully mobile, cooperation will be promoted. This is
because cooperators can gather in cooperative groups. Orbell and Dawes (1993) showed that in a
two-player social dilemma experiment with intergroup mobility, cooperation increases. This happens
since cooperators are more likely to expect that their partners are also cooperators. Yamagishi et al
(1994) supported it in computer simulations.
Based on these work, Ehrhart and Keser (1999) reported a cyclic process of the group
cooperation rate. They focus on the size and the average cooperation rate of groups. As the group
size increases, the group cooperation rate falls. Then, the group size decreases, which leads to the rise
of the group cooperation rate. We retest these results under various conditions.
In Section 2, we raise hypotheses. To test them, we design a laboratory experiment in Section 3.
In Section 4, we report results. Implications and future directions will be discussed in the final
section.
2. Method
2.1 Experimental Design
To test these hypotheses, we conduct a laboratory experiment. We use a similar experimental design
to Ehrhart and Keser (1999), with some differences (see Table 1). The crucial difference is that three
levels of mobility costs are compared: âhigh,â âlow,â and ânoâ mobility costs.
Sessions and Participants: Ten sessions in three Japanese universities in or near Tokyo. In
December 2003 and in June 2004. 17 participants in a session, with 170 participants in total.
Participants are undergraduate students. The experiment is announced in classes and by
advertisements on campus. There is no experienced participant, nor any deception.
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Conditions: High mobility costs in four sessions, low mobility costs in four sessions, and no mobility
costs in two sessions.
Procedure: 90 minutes per session. (i) Seats are assigned to participants by a lottery. In a large room
with no partition. (ii) Instruction by the experimenter and the pre-experiment questionnaire (30
minutes). (iii) The experiment. Participants are randomly assigned to groups by computer.
Participants are connected by a local area network on computer. Decisions are made anonymously.
They make decisions by clicking mousses on laptop computers (40 minutes). (iv) The
post-experiment questionnaire and debriefing (20 minutes). (v) Rewards are given.
Rewards: Participants receive monetary rewards (in yen), which is exactly how much payoff they
earned in the session. They know this. Still, they receive 1,000 yens as a minimum reward. They are
unaware of this adjustment. The average reward is 1244.8 yens (100 yens is about a U.S. dollar).
Instruction: An instruction handout is distributed. Participants keep it through a session. The
experimenter explains the experiment by reading the instruction. After that, participants are asked to
answer two confirmation tests. Solutions are provided.
2.2 Session
In a session, participants play a social dilemma game with intergroup mobility in four groups. A
session consists of two levels:
1. In a stage, participants play a social dilemma game.
2. In a round, they repeat five stages and then have an option to exit.
3. In a session, participants play 50 stages in 10 rounds.
Table 1. Differences of Experimental Design
Ehrhart and Keser (1999) This Paper Conditions No condition Three mobility costs Sessions 9 with 90 participants 10 with 170 participants Rounds and Exit Options 30, can create new group 10, cannot create Stages 30 50 Initial State 3 groups, each with 3 participants 4 groups, each with 4 or 5
participants Investment 10 units (dividable) 20 yens (undividable) Marginal Rate of Return 0.33 to 0.7 0.12 to 1 Mobility Costs 5 units 0, 20, 50 yens
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2.3 Social Dilemma Game in a Stage
In each stage, participants receive 20 yens as a resource. They decide whether to âprovideâ it to a
group as investment (cooperation) or to keep it (defection). The investment is multiplied. Then, it is
distributed equally to all the group members. Following Dawesâ (1980) formulation, payoff functions
are supposed to be linear (i.e., proportional to the number of providers).
Payoff functions: The rate of return depends on the group size. In single-player groups, the return is
equal to the investment. This is because there is no âsocialâ dilemma here.
u(C, m, 1) = u(D, m, 1) = 20 for any m,
where u(C) denotes the payoff of providing 20 yens when there are m providers in the group (except
the participant). Similarly, u(D) means that of keeping 20 yens.
. In two-player groups, the investment is multiplied by 1.5.
u(C, m, 2) = 302m = 15m, u(D, m, 2) = 30
2m + 20= 15m + 20.
In multiple-player groups, the investment is multiplied by 2.
u(C, m, n) = 40nm , u(D, m, n) = 40
nm + 20,
where n is the group size (see the graph with 4 participants).
Note that these payoff functions satisfy the conditions of social dilemmas (except that in
one-person groups).
Information: In each stage, a participant sees the following information on the computer display.
Payoff
Number of Cooperators (except the participant) m
Payoff of Providing u(C, m, 4) = 10 m
Payoff of Not Providing u(D, m, 4) = 10 m + 20
Social Dilemma
Exit Option
End
Start
95
Stage
Round
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1. number of providers in the group in the stage;
2. her decisions and payoffs in the round;
3. each group size, each groupâs average payoffs in the current stage, and those in the current
round.
2.4 Exit Option in a Round
After five stages, participants are simultaneously offered the exit option. Participants decide which
group to play the next round. They can stay at the same group. If another group is chosen,
participants pay 20 yens in the âlowâ mobility costs condition. They pay 50 yens in the âhighâ
mobility costs condition. It is free to move in the ânoâ mobility costs condition.
u(E) = â 50, u(S) = 0 in high mobility costs condition,
u(E) = â 20, u(S) = 0 in low mobility costs condition,
u(E) = u(S) = 0 in no mobility costs condition,
where u(E) expresses the payoff of exiting and u(S) does that of staying.
Information: After a round, participants are provided with the following information.
1. the payoff she earned in the round;
2. each groupâs average payoffs in each stage and the size;
3. each groupâs average payoffs in the current round;
In sum, a participant earns payoffs in a session as
ââ==
+9
1
50
1
)(),,(T
tT
t
tttt bunmau ,
where aT = C, D (cooperation or defection in stages) and bT = E, S (exit or stay in rounds).
3. Hypotheses
3.1 Effects of Group Size on Group Cooperation
In such a social dilemma, game theory predicts that cooperation declines as the group size increases.
This is because the marginal (per capital) rate of return decreases in bigger groups as follows.
u(C, m +1, 2) â u(C, m, 2) = 15,
u(C, m +1, n) â u(C, m, n) = n40 if n ⥠3.
Hypothesis 1 (Size on Cooperation). The bigger the group size is, the lower the group cooperation
rate will be. Conversely, the smaller the group size is, the higher the group cooperation rate will be.
3.2 Effects of Group Cooperation on Group Size
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What happens then? Once the group cooperation rate declines, rational actors would leave the group.
Hypothesis 2 (Cooperation on Size). The lower the group cooperation rate is, the smaller the group
size will be in the next round. Conversely, the higher the group cooperation rate is, the bigger the
group size will be in the next round.
Thus, we expect a cyclic process of the group size and the group cooperation rate.
3.3 Effects of Mobility Costs
Ehrhart and Keser (1999) already showed this process. So, we add the following hypothesis.
Hypothesis 3 (Mobility Costs). As mobility costs decrease, the cyclic process will be accelerated.
This is because players can move more easily if mobility costs lower.
4. Results
4.1 Descriptive Statistics
Descriptive statistics are provided in Tables 2 and 3. We are interested in mutual effects of the group
size and the group cooperation rate. So, the unit of analysis hereafter should be âthe group in the
Table 2. Descriptive Statistics of Sessions
Group Cooperation Rate
Group Mobility Rate Payoffs Session
Condition (Mobility
Costs)
Univ- ersity Year
Mean S.D. Mean S.D. Mean S.D. 1 50 yens A 04 0.349 0.209 0.203 0.180 1236.5 171.92 50 yens A 04 0.360 0.184 0.203 0.116 1228.2 113.83 50 yens B 03 0.256 0.181 0.209 0.201 1145.0 181.74 50 yens C 03 0.268 0.178 0.131 0.116 1203.9 142.45 20 yens A 04 0.295 0.161 0.327 0.145 1217.1 111.86 20 yens A 04 0.296 0.207 0.216 0.210 1223.7 102.57 20 yens A 03 0.395 0.224 0.281 0.162 1331.8 199.38 20 yens B 03 0.286 0.163 0.268 0.166 1218.8 88.19 0 yen A 04 0.288 0.231 0.693 0.181 1261.8 100.1
10 0 yen A 04 0.416 0.186 0.654 0.178 1381.2 138.3
Total 0.3
37 0.3
18 1265.5 Unit is individuals.
Group Cooperation
Group Size
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roundâ (with five stages and one exit option).
The sample size is 4 groups x 10 stages x 10 sessions = 400. If we use variables âin the previous
round,â the sample size becomes 360 (4 groups x 1 stage x 10 sessions = 40 is subtracted for the first
stage).
4.2 Effects of Group Size on Group Cooperation
In Hypothesis 1, the dependent variable is âthe average group cooperation rate in the current round.â
The independent variable is âthe current group size.â We control for the order of the round (1 to 9)
and the average group cooperation rate in the previous round. With these variables, we test the
hypothesis by a regression equation:
Current Cooperation = α + β1 Round + β2 Current Size + β3 Previous Cooperation.
Test results are shown in Table 4. In each condition, the current group size has significant
negative effects on the current group cooperation rate. This verifies the first hypothesis.
Result 1. The bigger the group size is, the lower the group cooperation rate is.
4.3 Effects of Group Cooperation on Group Size
Table 3. Descriptive Statistics of Conditions
Conditions (Mobility Costs)
50 Yens 20 Yens 0 Yens
Correlations Correlations Correlations
N Mean 1 2 N Mean 1 2 N Mean 1 2 1. Current Group Cooperation 160 0.34 160 0.36 80 0.40
2. Current Group Size 160 4.25 â0.32 160 4.25 â0.38 80 4.25 â0.30
3. Previous Group Cooperation 144 0.34 0.46 0.01 144 0.36 0.04 0.16 72 0.40 â0.13 0.39
Unit is group in round.
Table 4. Test Result of Hypothesis 1.
Conditions (Mobility Costs)
50 Yens 20 Yens 0 Yen Round .00 (.01) .00 (.01) â.02 (.01) Current Group Size â.04 (.01) *** â.05 (.01) *** â.03 (.01) * Previous Group Cooperation .47 (.07) *** .11 (.08) â.04 (.13) R2 .323 .160 .113 N=360. â p<.10, *p<.05, ** p<.01, ***p<.001. Unit is group in round. Unstandardized coefficients and standard errors. Dependent variable = Current group cooperation.
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In Hypothesis 2, the dependent variable is âthe current group size.â The independent variable is âthe
average group cooperation rate in the previous round.â We control for the order of the round and the
group size in the previous round. The hypothesis is tested by a regression equation:
Current Size = α + β1 Round + β2 Previous Cooperation + β3 Previous Size.
Test results are shown in Table 5. In each condition, the previous group cooperation rate has
significant positive effects on the current group size. This verifies the second hypothesis.
Result 2. The lower the group cooperation rate is, the smaller the group size is in the next round.
4.4 Effects of Mobility Costs on Cycle
By combining these results, we observe cyclic rises and falls of the group cooperation rate. As the
group expands, the group cooperation rate falls. As a result, the group shrinks, which on the other
hand raise the group cooperation rate.
How is this cycle affected by mobility costs? To test Hypothesis 3, compare regression
coefficients. Even as mobility costs increase, the effects of âthe current group sizeâ on âthe current
group cooperation rateâ have no trend (the coefficients are â.04 to â.05 to â.03, see Table 4). This
makes sense because once the group size is fixed, the group cooperation rate cannot be affected by
intergroup mobility.
On the other hand, the effects of â the previous group cooperationâ on âthe current group sizeâ
monotonically increase (2.12 to 3.11 to 4.83, see Table 5). This is a result of increasing intergroup
mobility.
Therefore, Hypothesis 3 is roughly supported. Still, differences are not statistically significant
(by testing differences of two independent groups).
Result 3. As mobility costs decrease, the cyclic process is accelerated. Still, this trend is not
statistically significant.
5. Conclusion
Table 5. Test Result of Hypothesis 2.
Conditions (Mobility Costs) 50 Yens 20 Yens 0 Yen
Round .00 (.04) â.01 (.05) .07 (.10) Previous Group Cooperation 2.12 (.44) *** 3.11 (.57) *** 4.83 (1.08) *** Previous Group Size .83 (.06) *** .65 (.07) *** .36 (.11) ** R2 .596 .374 .265 N=360. â p<.10, *p<.05, ** p<.01, ***p<.001. Unit is group in round. Unstandardized coefficients and standard errors. Dependent variable = Current Group Size.
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5.1 Summary
We examined how the group cooperation rate and the group size affect each other. Following Ehrhart
and Keser (1999), we conducted a social dilemma experiment with intergroup mobility. Unlike them,
we compared three mobility costs.
By analyzing the data at the group level, we reported the following findings.
(i) The group size decreases the group cooperation rate (Result 1). This is rather trivial because the
per capita marginal rate of return decreases as the group size increases.
(ii) The group cooperation rate boosts the group size in the next round (Result 2). This result can
only be attained when intergroup mobility is introduced.
(iii) Combining these results, we observed cyclic rises and falls of the group cooperation rate.
(iv) These three findings were already reported in Ehrhart and Keser (1999). What is added here is
that intergroup mobility accelerates the cycle (Result 3).
5.2 Practical Lesson
A practical lesson might be that, to raise cooperation in groups, it would be a useful method to
promote mobility. To keep a high cooperation level, restrain mobility. These could be applied in
business transactions, community development, and social movements.
5.3 Discussion
(i) Micro analyses: We analyzed the data at the âmacroâ group level. âMicroâ individual decisions
are analyzed in another paper (Fujiyama, Kobayashi, Koyama, and Oura 2004). The pre- and
post-experimental questionnaires will provide how individual fairness affects free-riding. Messick
and McClintock (1968) revealed that people sometimes have fair motivations rather than selfish ones.
Kobayashi (2001) argues that if such fairness is well shared, cooperation can be attained.
(ii) Network formation: This experiment may clarify the process of cooperative network formation.
Marwell and Oliver (1993) show that dense and centralized networks will promote cooperative
decisions. We can examine the reverse causality from cooperative behavior to cooperative networks.
(iii) Survey: Our experimental findings can be supplemented by field surveys on free-riding. March
and Simon (1958) argues that workers make two decisions: to participate or exit and to contribute or
not. We conducted a survey on workers. The survey focuses on the effect of mobility, yet such
effects have been unclear in previous surveys (i.e., Ostrom 1990 on communities and Takahashi 2001
on workplaces).
Group Cooperation Group CooperationGroup Size Group Sizeâ + â
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Appendix: Group Size and Group Cooperation Rate in Sessions
Session 1 (Mobility Costs = 50 Yens)
0
2
4
6
8
1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10
Round
Gro
up S
ize
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upC
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Group A Group B Group C Group D
Session 2 (Mobility Costs = 50 Yens)
02468
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1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 1000.20.40.60.811.2
Size Cooperation
Session 3 (Mobility Costs = 50 Yens)
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1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 100
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0.8
Size Cooperation
Session 4 (Mobility Costs = 50 Yens)
0
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1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 1000.20.40.60.811.2
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Session 6 (Mobility Costs = 20 Yens)
0
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1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 1000.20.40.60.811.2
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Session 7 (Mobility Costs = 20 Yens)
02468
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1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 1000.20.40.60.811.2
Size Cooperation
Session 8 (Mobility Costs = 20 Yens)
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1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 1000.20.40.60.811.2
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Session 5 (Mobility Costs = 20 Yens)
024
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1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 1000.20.4
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References Axelrod, Robert. 1984. The Evolution of Cooperation. New York: Basic Books.
Dawes, Robyn M. 1980. âSocial Dilemmas.â Annual Review of Psychology 31:169-93.
Ehrhart, Karl-Martin and Claudia Keser. 1999. âMobility and Cooperation: On the Run.â CIRANO Working Papers
99s-24.
Fujiyama, Hideki, Jun Kobayashi, Yuhsuke Koyama, and Hirokuni Oura. 2004. âSocial Dilemma and Intergroup
Mobility: Experimental Analysis.â Paper presented at the 8th China-Japan Symposium on Statistics. October 17.
Guilin, China.
Hirschman, Albert O. 1970. Exit, Voice, and Loyalty: Responses to Decline in Firms, Organizations and States.
Cambridge, MA: Harvard University Press.
Kobayashi, Jun. 2001. âUnanimous Opinions in Social Influence Networks.â Journal of Mathematical Sociology
25:285-97.
Kollock, Peter. 1998. âSocial Dilemmas: The Anatomy of Cooperation.â Annual Review of Sociology 24:183-214.
March, James G. and Herbert Simon. 1958. Organizations. New York: John Wiley and Son.
Marwell, Gerald and Pamela Oliver. 1993. The Collective Mass in Collective Action: A Micro-Social Theory.
Cambridge: Cambridge University Press.
Messick, David M. and Charles Graham McClintock. 1968. âMotivational Bases of Choice in Experimental Games.â
Journal of Experimental Social Psychology 4(1): 1-25.
Olson, Mancur. 1965. The Logic of Collective Action: Public Goods and the Theory of Groups. Harvard University
Press.
Session 9 (Mobility Costs = 0 Yens)
0
2
4
6
8
10
1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 1000.20.40.60.811.2
Size Cooperation
Session 10 (Mobility Costs = 0 Yens)
0
5
10
15
1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 1000.20.40.60.811.2
Size Cooperation
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Orbell, John M. and Robyn M. Dawes. 1993. âSocial Welfare, Cooperatorsâ Advantage, and the Option of Not
Playing the Game.â American Sociological Review 58, 787-800.
Ostrom, Elinor. 1990. Governing the Commons: The Evolution of Institutions for Collective Action. New York:
Cambridge University Press.
Takahashi, Nobuo. 2001. âEffective Temperature Hypothesis and Lukewarm Feeling in Japanese Firms.â
International Journal of Management Literature 1: 127-42.
Tiebout, Charles M. 1956. âA Pure Theory of Local Public Expenditures.â Journal of Political Economy 64: 416-24.
Yamagishi, Toshio, Nahoko Hayashi, and Nobuhito Jin. 1994. âPrisoner's Dilemma Network: Selection Strategy
versus Action Strategy.â In Ulrich Schulz, Wulf Alberts, and Ulrich Mueller (eds.), Social Dilemmas and
Cooperation, pp.233-50, Berlin: Springer-Verlag.
Acknowledgement: Authors thank Authors thank Gary S. Becker, Phillip Bonacich, Vincent Buskens, Toko Kiyonari, Nobuyuki Takahashi, Toshio Yamagishi, and Kazuo Yamaguchi for their comments. We also thank Hideki Ishihara, Kazuhiro Kagoya, Masayuki Kanai, Hideki Kamiyama, Naoko Taniguchi, Ryuhei Tsuji, Motoko Harihara, and Masayoshi Muto for their support in the experiment.
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Decisions on the Exit Micro Analyses of a Social Dilemma Experiment with
Intergroup Mobility 1
Hideki Fujiyama, Jun Kobayashi, Yuhsuke Koyama, and Hirokuni Oura (Dokkyo University) (University of Chicago) (Tokyo Institute of Technology)
(Teikyo University)
Abstract: Using experimental data from a series of social dilemma experiments, we examine the differences in the exit
behaviors between cooperators and non-cooperators. Our results indicate that cooperators have a higher
probability for an exit choice than non-cooperators. Non-cooperators, on the other hand, are more sensitive to
the surrounding cooperation rate in their group.
Keywords: exit, decision-making, social dilemmas, mobility, experiment.
1. Introduction
In modern societies, we enjoy increasing mobility in areas such as job changes, moves and immigration.
On the other hand, there exists the free-riding problem, such as shirking in the workplaces and issues
relating to public peace and order.
Theoretically, there is a relationship between these two phenomena, that is, there is the negative
effect of mobility on cooperation. In situations where there is no mobility, players continue to interact
with each other in their groups or societies. They know that free-riding can brings about harmful effects
on the their future payoff. In situations where there is mobility, however, players can cut relationships
with other members of their group. The more mobility increases, the less the players care about the
harmful effects of free riding. This argument is based on the âfolk theoremâ of the repeated prisoner
dilemma game.
On the other hand, the positive effect of mobility on cooperation is shown in several papers on the
coordination game (Dieckmann[1999], Bhaskar and Vega-Redondo [2004], Oechssler [1997]). In the
coordination game, there are both a Pareto-efficient equilibrium and a Pareto-inefficient equilibrium. As
the Pareto inefficient equilibrium can have the advantage in risk taking, that is ârisk dominance,â the
Pareto inefficient and risk dominant equilibrium is selected under many learning processes (Kandori et al
[1993], Young [1993]). However, if there is a choice to move to another group, the Pareto efficient
equilibrium is selected instead of the inefficient and risk dominant equilibrium. The logic is very simple.
The player in the inefficient group can exit in order to change the action from the inefficient one to the
efficient one.
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However, this logic in the coordination game does not apply in the social (or prisoner) dilemma game.
In the coordination game, as all players wish to change for the efficient action, the action of players who
are moving to a group is desirable for players who have been in the group. On the other hand, in the social
(or prisoner) dilemma game, some players try to enjoy free riding by moving to another group. The
cooperative players in the group do not continue to cooperate because of these free riders. The equilibrium
efficiency is therefore affected.
In the social (or prisoner) dilemma game, therefore, it is important for cooperators to continue to exit
from inefficient groups earlier than the non-cooperators (or free riders). In other words, the difference in
moving behaviors between cooperators and non-cooperators is a key factor in achieving cooperation in a
social dilemma situation with mobility.1 We estimate the exiting functions and examine the differences in moving behaviors between
cooperators and non-cooperators using our experimental data.
In Section 2, we outline the experimental design and the data set. Section 3 reports the results and
Section 4 concludes the paper. 2. Research design
2.1 The Experiment
Social Dilemma with Intergroup Mobility Dawes (1980) gives a formal definition of social dilemmas. In a social dilemma,
1. persons have options of âcooperationâ (voluntary contribution to the group) and ânon-cooperationâ (non-contribution);
2. non-cooperation always provides higher payoff than cooperation 3. but if everyone defects, they receive less payoff than if everyone cooperates.
Payoff is measured in an objective material scale. We are interested in social dilemmas with intergroup mobility. In the our experiment, we assume:
1. in a stage, participants play a social dilemma game in groups; 2. in a round, they repeat five stages and then have an option to move to another group; 3. in a session, they repeat ten rounds.
In total, participants play the social dilemma game for 50 stages with nine chances to exit (Figure 1.).
1 Ehrhart and Kaser [1999] reports that the cooperators are on the run from non-cooperators who follow them
around.
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Figure 1: Structure of the Game.
We control mobility costs. Four levels of mobility costs are compared: âhigh,â âlow,â and âzeroâ mobility costs and âno mobilityâ condition.
Sessions: Ten sessions were held in three Japanese universities in or near Tokyo in December 2003 and in June 2004. In each session, 17 or 16 participants were enrolled, with a total of 234 participants in 14 sessions.
Conditions: (i) 0-yen-moving-cost (4 sessions with 17 participants) (ii) 20-yen-moving-cost (4 sessions with 17 participants) (iii) 50-yen-moving-cost (4 sessions with 17 participants) (iv) no mobility i.e. no moving option (4 sessions with 16 participants).
Participants: 234 undergraduate students. The experiment was announced in classes and by advertisements on campuses. There were no experienced participants, nor was there any deception.
Procedure: (i) Seats were assigned to participants by a lottery in a large room with no partitions. (ii) Instructions, and a pre-examination questionnaire, were given by the experimenters. (iii) Decisions were made anonymously. (iv) A post-experiment questionnaire and debriefing were given. (v) Rewards were given.
Time: 90 minutes per session. 30 minutes for the instruction and the pre-experimental questionnaire. 40 minutes for the experiment. 20 minutes for the post-experimental questionnaire and debriefing.
Rewards: Participants knew that they would receive a monetary reward (in yen), which would be exactly equal to the payoff they earned in their session. However, they did not know that they would receive a 1,000 yen as a minimum reward, regardless of their earnings. The average reward was 1287.1 yen, with the standard deviation of 190.1 yen (a 100 yen was about one U.S. dollar at the time of the experiment).
Equipment: Participants were connected by computers on a local area network. They made decisions by clicking their mouse on a laptop computer.
Instructions: An instruction handout was distributed. Participants kept it through out the session. The experimenter explained the experiment by reading the instructions. Participants were then asked to complete two confirmation tests, in order to check they had understood the instructions. Solutions were provided.
Social Dilemma
Exit Option
End
Start
95
Stage
Round
128
Matching: Participants were randomly assigned to groups by computer. Each group had four or five participants at the beginning.
Social Dilemma Game in a Stage In a session, participants played social dilemma games with intergroup mobility in four groups. The game consisted of two levels:
1. In each stage, participants played a social dilemma game. 2. In a round, they repeated five stages and then had an option to exit.
Participants played 50 stages in nine rounds. In each stage, participants received 20 yen as a resource. They decided whether to âprovideâ it to
their group as an investment (cooperation), or to keep it (non-cooperation). The investment was multiplied by 2 or 1.5, depending on their group size. It was then distributed equally to all the group members.
Payoff functions: The rate of return depended on the group size. In single-player groups, the return was equal to the investment. This was because there was no âsocialâ dilemma:
u(C) = u(N) = 20,
where u(C) denotes the payoff of providing 20 yen, while u(N) means keeping 20 yen.
In two-player groups, the investment was multiplied by 1.5:
u(C) = 302m
= 15m, u(N) = 302m
+ 20= 15m + 20,
where there were m providers in the group.
In multiple-player groups, the investment was multiplied by 2:
u(C) = 40nm
, u(N) = 40nm
+ 20,
where n was the group size (see the graph for 4 participants). Note that these payoff functions satisfy the conditions of social dilemmas except that for one-person groups (Figure 2).
Figure 2: Social Dilemmas
Information: Participants made decisions anonymously. In each stage, a participant saw the following information on the computer display:
1. The number of providers in the group in the stage; 2. His/her decisions and payoffs in the round; 3. Each groupâs size, each groupâs average payoffs in the current stage and each groupâs average
payoffs in the current round.
Payoff
Cooperators m
Payoff of Cooperation u(C) = 10
Payoff of Non-cooperation u(N) = 10 m + 20
129
Exit Options/Pauses in a Round Exit option: After five stages, participants were simultaneously offered an exit option. Participants decided which group to join in the next round. They could decide to stay in the same group. If another group was chosen, participants paid 20 yen costs in the âlowâ mobility costs condition, 50 yen in the âhighâ mobility costs condition and no cost for moving in the ânoâ mobility costs condition:
u(E) = â 50, u(S) = 0 in high mobility costs condition,
u(E) = â 20, u(S) = 0 in low mobility costs condition,
u(E) = u(S) = 0 in no mobility costs condition, where u(E) expresses the payoff for exiting, and u(S) for staying. Pause: In the âno mobilityâ condition, participants make a pause for a minute. During this time, they see the same information as shown in other conditions.
u(S) = 0.
Information: In any condition, after a round participants were provided with information on: 1. The payoff he/she earned in that round; 2. Each groupâs average payoffs in each stage and the sizes of the groups; 3. Each groupâs average payoffs in the current round;
In summary, a participant earned payoffs in a session as follows:
ââ==
+9
1
50
1)()(
T
T
t
t buau ,
where a = C, N (cooperation or non-cooperation in stages), and b = E, S (exiting or staying in a round).
2.2 Data and Estimation
Data
A player has nine chances to exit from a group in a session. There are ten sessions in which 17
participants are included. The sample size is 1,530 (= 9 chances Ã17 participants Ã10 sessions). We
construct an âexit variable,â that is, if a participant exits from a group then the value is 1, otherwise, it is
0. That is, this variable is a binary.
The degree of individual cooperation is represented by the âindividual cooperation rate,â which is
the ratio of cooperation in all 50 decisions. This measure is not concerned with attitudes, but with
behaviors.
In order to investigate whether there is a difference in exit behaviors between cooperators and
non-cooperators, we estimate the relationship between decisions on exit and âindividual cooperation
rates.â We assume that the âexit variableâ is a dependent variable, and that the âindividual cooperation
rateâ is an explanatory variable. As the âexitâ is not a direct significant factor that affects the âindividual
cooperation rateâ in this experiment (Fujiyama et al [2005]), we assume this relationship.
In order to control the environment, we consider several control factors. The first control factor is
one in which participants are pushed to another group. For this factor, we have a âgroup surrounding
cooperation rate,â which is the groupâs average cooperation rate excluding the concerned participant in
that round. For example, there are four participants in a group, and the cooperation rate of Participant 1 is
130
0.4; the cooperation rate of Participant 2 is 0.6; the cooperation rate of Participant 3 is 0.2; and the
cooperation rate of Participant 4 is 0.3. For Participant 2, the âgroup surrounding cooperation rateâ is 0.3
(=(0.4+0.2+0.3)/3). If this value is low, then the participant tends to exit from the group.
The second control factor is one in which participants are pulled from other groups. For this
factor, we have data for payoffs of the other groups in the current round. This information is
interpreted as a simple predicted average payoff for each group, that is, we assume that participants
consider that the payoff in a current round significantly affects the payoff in the next round (Figure
3).2 Though there are more complicated (sophisticated) ways of predicting outcomes, the fact that participants have no prior experience of playing the game means that they utilize our simple
prediction methods, and these are therefore a reasonable way to analyze the results.
Figure 3: Simple Prediction
From the point of view of maximizing payoff, the first and second factors mentioned above are the
most important pieces of information. The reason we take the cooperation rate in âpushâ factor and
payoffs in âpullâ factor is as follows: (1) The payoff is determined by the âgroup surrounding cooperation
rateâ and the concerned participantâs cooperation rate. There is therefore, by definition, positive
2 If there is an empty group in a current round, that is, there is no participant in that group, we take 20 yen as the
predicted payoff for that group. This is because, if one participant moves to that empty group in the next round, but
all other participants stay in the same groups, then the participant belongs to the one participant group in the next
round, and the participantâs payoff is, by definition, 20 yen.
Current Round
Next Round
group A group B group C group D
Concerned Participant
Realized Payoff Realized Payoff Realized Payoff
Simple Prediction
Simple Prediction
Simple Prediction
131
correlation between these two explanatory variables (individual cooperation and individual payoff). (2)
There is no such correlation concerning âpullâ factors. In addition, the average payoffs of other groups are
displayed on their computer screens for all participants in the experiment.
The third control factor is the sizes of the other groups, and the dummy variables for the 50-yen-cost
and 0-yen-cost conditions.3 We omit the data for the exits from one and two participants groups for two reasons: the formula for payoffs in one and two participant groups are different and it is not relevant to
treat the âgroup surrounding cooperation rateâ as in other cases.4 The relationship among variables is summarized in Figure 4.
1ïŒExit
0ïŒNot Exit
Constant Term Control Variables
Push Factor: (Groupâs cooperation rate except the player)
Pull Factor: (Other groupsâ payoffsïŒMax/Middle/Min)
Other FactorsïŒ
Figure 4: Dependent and Explanatory Variables
Estimations
We consider two estimations. (1) A simple estimation using all data. (2) An estimation in which we divide
data into two categories, that is, high cooperators and low cooperators, to compare estimated parameters.
We arrange the data in order, from high individual cooperation rates to low individual cooperation rates,
and consider that the upper one-third of the data is data for high cooperators, and the lower one-third of
the data is data for low cooperators. As the dependent variable (âthe exit variableâ) is binary data, we use
the Probit and Logit models to estimate parameters. We consider that there is not serious multicollinearity,
3 As the total number of participants is fixed, we omit, from our analysis, the total number of participants in the
group to which the concerned participant belongs. If we include this variable, there is perfect correlation among the
four variables (the number of participants in the concerned group, plus the numbers of participants in the other three
groups).
4 In one-participant groups, it is impossible to calculate the âgroup surrounding cooperation rateâ. In a
two-participant group, a participant can retaliate against another participant directly. This direct retaliation is
impossible in three-or-more-participant groups. From this point of view, we can consider that games of
two-participants, and three-or-more-participant, are qualitatively different.
Individual Cooperation Rate
(Moving Cost conditionsïŒ50 yen / 0 yen Dummies)
(Other groupsâ sizeïŒMax/Middle/Min)
132
as for the explanatory variables, all correlation coefficients are under 0.3, and all VIFs are under 1.5
generally.5
3. Results
The result of the estimation is shown in Table 1.6
Table 1 : Decision on the Exit
Dependent Variable: Exit Variable Variables Coefficients (P-value)
Constant Term Individual Cooperation Rate Group Surrounding Cooperation Rate Other Groupâs Payoff (Max) Other Groupâs Payoff (Mid) Other Groupâs Payoff (Min) Other Groupâs Size (Max) Other Groupâs Size (Mid) Other Groupâs Size (Min) Dummy for 50 yen moving cost Dummy for 0 yen moving cost
-1.135 (0.028)* 0.513 (0.006)**
-1.442 (0.000)** 0.010 (0.327) 0.036 (0.031)*
-0.026 (0.231) 0.008 (0.793) 0.028 (0.432) 0.024 (0.571)
-0.375 (0.000)** 1.068 (0.000)**
Probit Estimation
LR test (zero slopes) =266.186 (P-value =0.000**)
N=1425, 2R =0.183, Fraction of Correct Prediction =0.734. * Significant at 5 %, ** Significant at 1%.
From this estimation, we obtain the following results:
[Result 1] There is a positive correlation between the âindividual cooperation rateâ and the probability for
the exit choice.
[Result 2] There is a negative correlation between the âgroup surrounding cooperation rateâ and the
probability for the exit choice.
In order to examine the difference between the higher cooperators and the lower cooperators, we
arrange in descending order all participants in terms of the âindividual cooperation rate,â and divide data
into three equal categories. As a result, participants whose âindividual cooperation ratesâ are higher than
0.4 belong to the upper one-third of the data. Participants whose âindividual cooperation ratesâ are lower
5 Among the other group payoffs, we found the correlation coefficients are about 0.5, and VIFs are about (but under)
2. However, these variables are control variables that we does not focus on in our analysis.
6 We have the similar results in the Logit model.
133
than 0.2 belong to the lower one-third of the data. We compare upper and lower categories. The LR test
for structural changes of all variables indicates that the null hypothesis, under which there is no difference
between these two categories, is rejected with a level of 1 % significance.
[Result 3] There are significant differences in the exit decision-making processes between the upper
one-third of participants and the lower one-third of participants in terms of the âindividual cooperation
rate.â
With dummy variables for the lower one-third of the data, we estimate the difference more concretely.
The result is shown in Table 2.
Table 2 : Difference between high and low cooperators
Dependent Variable: Exit Variable Variables Coefficients (P-value)
Constant Term (CT) Individual Cooperation Rate (ICR) Group Surrounding Cooperation Rate (GSCR) Other Groupâs Payoff [Max] (OGPMAX) Other Groupâs Payoff [Mid] (OGPMID Other Groupâs Payoff [Min] (OGPMIN) Other Groupâs Size [Max] (OGSMAX) Other Groupâs Size [Mid] (OGSMID) Other Groupâs Size [Min] (OGMIN) Dummy for 50 yen moving cost (D50) Dummy for 0 yen moving cost (D0) Structural Change Dummy for CT Structural Change Dummy for ICR Structural Change Dummy for GSCR Structural Change Dummy for OGPMAX Structural Change Dummy for OGPMID Structural Change Dummy for OGPMIN Structural Change Dummy for OGSMAX Structural Change Dummy for OGSMID Structural Change Dummy for OGSMIN Structural Change Dummy for D50 Structural Change Dummy for D0
-0.774 (0.386) 1.445 (0.009)**
-0.699 (0.035)* 0.003 (0.877) 0.017 (0.565)*
-0.018 (0.625) -0.028 (0.558) -0.042 (0.468) -0.018 (0.805) -0.400 (0.008)** 0.747 (0.000)**
-0.921 (0.505) 0.251 (0.834)
-1.958 (0.001)** 0.001 (0.958) 0.008 (0.846)
-0.002 (0.968) 0.117 (0.138) 0.174 (0.064) 0.199 (0.070)
-0.200 (0.366) 0.462 (0.074)
Probit Estimation
LR test (zero slopes) =184.699 (P-value =0.000**)
N=910, 2R =0.194, Fraction of Correct Prediction =0.730. *Significant at 5 %, ** Significant at 1%.
From this estimation, we have the following result:
[Result 4] The structural change dummy for the âgroup surrounding cooperation rateâ has a significant
and negative coefficient. In other words, the graph for the participants with low âindividual cooperation
ratesâ has a steeper negative slope than that for the participants with a high âindividual cooperation rate.â
134
To see the difference more clearly, we show graphs of the probability for the exit choice. In Figure 5,
we substitute the values of the constant term and the âgroup surrounding cooperation rateâ into the
estimated cumulative density function.7 In Figure 6, in addition to these values, we also substitute the average values of explanatory variables into the estimated cumulative density function.
0.2 0.4 0.6 0.8 1GSCR
0.1
0.2
0.3
0.4
0.5
Prob .for Exit
Low Coop .
High Coop .
Figure 5: Probability for Exit (only constant term)
0.2 0.4 0.6 0.8 1GSCR
0.1
0.2
0.3
0.4
0.5
Prob .for Exit
Low Coop .
High Coop .
Figure 6: Probability for Exit (all explanatory variables)
4. Conclusion
We investigated factors in the exit decision-making and derived the following conclusions:
First, the surrounding cooperation rate in their group was an important factor for all participants
(Result 2). Cooperators have a higher probability for the exit choice (Result 1, Figure 5, Figure 6). One
reason for this phenomenon is that cooperators have a very high threshold of the surrounding cooperation
7 As we divide the data into two categories, in terms of the âindividual cooperation rate,â average values of
âindividual cooperation rateâ in both categories are included in the constant term.
135
rate in their group, so the cooperators tends to exit from groups in general. In other words, the cooperators
ask a high cooperation rate for others as same as themselves, so the cooperator is not satisfied with the
middle (or possibly high) cooperation rate. As a result, the cooperators have high probability for the exit
choice.
Second, there is a significant difference in the exit behavior of the cooperators and in that of the
non-cooperators (Result 3). Non-cooperators are more sensitive to the surrounding cooperation rate in
their group (Result 4). One reason for this phenomenon is that non-cooperators attempt free riding. At the
low surrounding cooperation rate in their group, they exit to other groups because they cannot enjoy free
riding. At the middle or high surrounding cooperation rate, they do not exit to other groups because they
enjoy free riding. In other words, for the non-cooperators, the surrounding cooperation rate in their group
is the primary factor for the exit decision. This is the reason for this sensitivity.
Finally, we can derive a practical lesson from the above conclusions. Cooperators exit from the
groups before the groupâs cooperation rates do not decrease so much. After the cooperators exit,
non-cooperators begin to exit. Therefore, in order to achieve the high cooperation rate, it is important to
create a new group and enclose cooperators in early stages. References Bhaskar, V and Fernando Vega-Redondo. 2004. âMigration and the evolution of conventions.â Journal of Economic
Behavior & Organization 55 397-418.
Dieckmann, Tone. 1999. âThe evolution of conventions with mobile players.â Journal of Economic Behavior &
Organization 38 93-111.
Dawes, Robyn M. 1980. âSocial Dilemmas.â Annual Review of Psychology 31:169-93.
Ehrhart, Karl-Martin and Claudia Keser. 1999. âMobility and Cooperation: On the Run.â CIRANO Working Papers
99s-24.
Fujiyama, Hideki, Jun Kobayashi, Yuhsuke Koyama, Hirokuni Oura. 2005. âPerformance of the Exit: Micro analyses
of a Social Dilemma Experiment with Intergroup Mobility 2.â in this volume.
Kandori, M., Mailath, G., Rob, R.1993. âLearning, mutation, and long-run equilibria in games.â Econometrica 61
29-56.
Oechssler, Jorg 1997 âDecentralization and the coordination problem.â Journal of Economic Behavior &
Organization 32 119-135.
Orbell, John M. and Robyn M. Dawes. 1993. âSocial Welfare, Cooperatorsâ Advantage, and the Option of Not
Playing the Game.â American Sociological Review 58, 787-800.
Young, P. H. 1993. âThe evolution of conventions.â Econometrica 61, 57-84.
Acknowledgement: Authors thank Authors thank Gary S. Becker, Phillip Bonacich, Vincent Buskens, Toshio Yamagishi, and Kazuo Yamaguchi for their comments. We also thank Hideki Ishihara, Kazuhiro Kagoya, Masayuki Kanai, Hideki Kamiyama, Naoko Taniguchi, Ryuhei Tsuji, Motoko Harihara, and Masayoshi Muto for their support.
136
Performance of the Exit Micro Analyses of a Social Dilemma Experiment with
Intergroup Mobility 2
Hideki Fujiyama, Jun Kobayashi, Yuhsuke Koyama, and Hirokuni Oura (Dokkyo University) (University of Chicago) (Tokyo Institute of Technology)
(Teikyo University)
Abstract: We investigate the results of exit choices on three variables: the group surrounding cooperation rate, the
individual cooperation rate and the individual payoff. As a result of these exit choices, the participants, on
average, succeeded in moving into more cooperative groups. However, the scale of this success was small, and
did not dominate the cost of the exit options, 20 yen or 50 yen.
Keywords: exit, result, social dilemma, mobility, experiment.
1. Introduction
Mobility affects the social dilemma both positively and negatively. The cooperation rate in a group
depends on whether cooperators can select cooperators from all players, or not.
This selection effect is supported indirectly by an experimental analysis (Orbell and Dawes[1993]) .
In their experiment, participants can choose between playing and not playing Prisonerâs Dilemma games.
If this choice exits, then cooperators tend to play the games, and as a result, cooperators tends to meet
with each other.
Fujiyama et al [2005a] shows that there is a significant difference in decision-makings between
cooperators and non-cooperators. Cooperators tend to exit more than non-cooperators. On the other hand,
non-cooperators are more sensitive to the cooperation rates around them. In addition, Fujiyama et al
[2005b] showed that there are significant different intentions of the exit choice between cooperators and
non-cooperators. Non-cooperators tried to move into the groups with higher payoffs. On the other hand,
there is not such a tendency in cooperators. In order to evaluate these behaviors, it is important to estimate
the performance of the exit choice.
We examine the results of the exit on various variables: the group surrounding cooperation rate, the
individual cooperation rate, the individual payoff, and the group size.
In Section 2, we outline the data set. Section 3 reports the results and Section 4 concludes the paper. 2. Research design
137
2.1 The Experiment
This subsection is the same as the subsection 2.1 in Fujiyama et al [2005 a], which is included in this
volume. See the corresponding subsection.
2.2 Data and Estimation
Data
A player has nine chances to exit from a group in a session. There are ten sessions in which 17
participants are included. The sample size is 1530(=9 chances Ã17 participants à 10sessions). We
construct an âexit variable, â that is, if a participant exits from a group then the value is 1, otherwise, it is
0. This binary variable is a target explanatory variable.
We consider four different models in which dependent variables differ. In the first model, a
dependent variable is a âgroup surrounding cooperation rate,â which is a groupâs average cooperation
rate excluding the concerned participant in that round. For example, there are four participants in a group
and the cooperation rate of Participant 1 is 0.4; the cooperation rate of Participant 2 is 0.6; the cooperation
rate of Participant 3 is 0.2; and the cooperation rate of Participant 4 is 0.3. For Participant 2, the âgroup
surrounding cooperation rateâ is 0.3(=(0.4+0.2+0.3)/3). In the second model, a dependent variable is an
âindividual cooperation rate in a round,â which is a cooperation rate of a concerned participant in a
round. In the third model, a dependent variable is an âindividual payoff in a round,â which is the
concerned participantâs average payoff per social dilemma game in a round. In the forth model, a
dependent variable is the âgroup sizeâ in a round.
In order to control the environment, we consider dummy variables for 50-yen-cost and 0-yen-cost
conditions and a trend dummy variables. The trend dummy variable represents a decreasing in
cooperation rates that is observed generally.8 In addition to these variables, as the payoff function is different; we consider dummy variables for a one-participant group and a two-participant group.
In order to examine the performance of the exit choice, we collect the âexit variableâ in a current
round and the dependent and control variables in the next round (Figure 1).
8 This decline in the cooperation is reported in many experiments (Dawes and Tharler [1988]).
138
Figure 1: Data
Estimations
We consider four models in which dependent variables differ. In the first model (Model I), the âgroup
surrounding cooperation rateâ is a dependent variable. In this model, we examine whether the exit made
the circumstance better or not. There are seven control variables (the 50-yen-cost dummy, the 0-yen-cost
dummy, the trend, the âgroup sizeâ, the one-participant group dummy, the two-participant group dummy,
the âindividual cooperation rate in a roundâ). These control variables are divided into three classes. The
50-yen-cost dummy, the 0-yen-cost dummy and the trend are common in session. The âgroup sizeâ, the
one-participant group and the two-participant group are common in a round and decided before the first
stage in a round. The âindividual cooperation rate in a roundâ is decided in a round endogenously.
In the second model (Model II), the âindividual cooperation rate in a roundâ is a dependent variable.
In this model, we examine whether participants who exit change their cooperative behaviors or not. All
control variables are the same as the control variables in the first model except for âindividual cooperation
rate in a round.â The âgroup surrounding cooperation rateâ is included instead of the âindividual
cooperation rate in a round.â
In the third model (Model III), the âindividual payoff in a roundâ is a dependent variable. In this
group A group Dgroup Cgroup B
a collection of data
a collection of data 1
0
realized values
ã» individual cooperation rate in a round
ã» individual payoff in a round
ã» group surrounding cooperation rate
ã» group size
ã» dummy for one-participant group
ã» dummy for two-participant group
Not Exit (0) or Exit (1)
139
model, we examine whether the participants who exit improve their payoff or not. This is a direct
estimation on a performance of the exit option. The âindividual payoff in a roundâ is determined by the
âindividual cooperation rate in a roundâ and the âgroup surrounding cooperation rate.â As it is difficult to
extract changes that are caused by the exit choice from all changes, we omit these two variables. In
addition, we consider an âexit variableâ as a proxy variable for these two variables and the coefficient of it
as direct and indirect effects of an exit choice. There are six control variables (50-yen-cost dummy,
0-yen-cost dummy, trend, group size, one-participant group dummy, two-participant group dummy). It is
important to note that in this analysis the âindividual payoff in a roundâ does not include the moving costs,
that is, we use data for the gross payoffs.
In the fourth model (Model IV), the âgroup sizeâ is a dependent variable. In this model, we examine
an effect of the exit on the âgroup size.â The âgroup sizeâ is an important factor in social dilemma game
because it is known that the group size affect the cooperation rates negatively (Olson [1965], Kollock
[1998]), and that the cooperators move to the small size group (Ehrhat and Kaser[1999]). As the âgroup
sizeâ is determined before the first stage in a round, we cannot use the control variables that is determine
in the round endogenously. Therefore, there are only three control variables (50-yen-cost dummy,
0-yen-cost dummy and trend).
As for explanatory variables, all correlation coefficients are under 0.3 and the VIFs are under 1.5.
Therefore, we consider that there is not a serious multicollinearity.
3. Results
In Model I, we examine the effect of the exit on the âgroup surrounding cooperation rate.â The result of
the estimation is shown in Table 1.
Table 1: Effect on the âgroup surrounding cooperation rateâ
Dependent Variable: Group Surrounding Cooperation Rate Variables Coefficients (P-value)
Constant Term Exit Variable Individual Cooperation Rate in a Round Group Size Dummy for 50 yen moving cost Dummy for 0 yen moving cost Trend Dummy for One Participant Group Dummy for Two Participant Group
0.405 (0.000)** 0.028 (0.009)** 0.242 (0.000)**
-0.026 (0.000)** -0.007 (0.501) 0.020 (0.140) -0.007 (0.000)** -0.496 (0.000)** 0.063 (0.000)**
OLS estimation
F (zero slopes)=72.22 (P-value =0.000**)
N=1530, adj- 2R =0.271 * Siginificant at 5 %, ** Significant at 1 %.
140
With this estimation, we have a result as follows:
[Result 1] There is a significant positive correlation between the âexit variableâ and the âgroup
surrounding cooperation rate.â We have the data for âgroup surrounding cooperation rateâ after the
decision making on the exit option (Figure 1), we have the result that there is a positive effect of the âexitâ
on the âgroup surrounding cooperation rate.â
As there are interesting results concerning the control variables, we summarize them as follows:
[Result 2] There is a significant positive correlation between the âindividual cooperation rate in a roundâ
and the âgroup surrounding cooperation rate.â
[Result 3] There is a significant negative correlation between the âgroup sizeâ and the âgroup surrounding
cooperation rate.â The group size is determined before the âsurrounding cooperation rateâ is determined,
we have the result that there is a negative effect of the âgroup sizeâ on the âsurrounding cooperation rate.â
In Model II, we examine the effect of the exit on the âindividual cooperation rate in a round.â The
result of the estimation is shown in Table 2.
Table 2: Effect on the âindividual cooperation rate in a roundâ
Dependent Variable: Individual cooperation rate in a round Variables Coefficients (P-value)
Constant Term Exit Variable Group Surrounding Cooperation Rate Group Size Dummy for 50 yen moving cost Dummy for 0 yen moving cost Trend Dummy for One Participant Group Dummy for Two Participant Group
0.269 (0.000)** 0.022 (0.151) 0.497 (0.000)**
-0.017 (0.000)** -0.006 (0.661) 0.013 (0.502)
-0.047 (0.078) 0.319 (0.000)**
0.041 (0.217)
OLS estimation
F (zero slopes)=46.98 (P-value =0.000**)
N=1530, adj- 2R =0.198 * Siginificant at 5 %, ** Significant at 1 %.
With this estimation, we have a result as follows:
[Result 4] There is not a significant correlation between the âexit variableâ and the âindividual
cooperation rate in a round.â
141
As there are interesting results concerning the control variables, we summarize them as follows:
[Result 5] There is a significant positive correlation between the âindividual cooperation rate in a roundâ
and the âindividual cooperation rate in a round.â
[Result 6] There is a significant negative correlation between the âgroup sizeâ and the âindividual
cooperation rate in a round.â The group size is determined before the âindividual cooperation rate in a
roundâ is determined, we have the result that there is a negative effect of the âgroup sizeâ on âindividual
cooperation rate in a round.â
In Model III, we examine the direct and indirect effects of the exit on the âindividual cooperation rate
in a roundâ omitting the variables the âgroup surrounding cooperation rateâ and the âindividual
cooperation rate in a round.â The result of the estimation is shown in Table 3.
Table 3: Effect on the âindividual payoff in a roundâ
Dependent Variable: Individual Payoff in a Round Variables Coefficients (P-value)
Constant Term Exit Variable Group Size Dummy for 50 yen moving cost Dummy for 0 yen moving cost Trend Dummy for One Participant Group Dummy for Two Participant Group
30.70 (0.000)** 0.773 (0.018)* -0.704 (0.000)**
-0.233 (0.464) 0.458 (0.263) -0.188 (0.001)** -9.514 (0.000)** -3.541 (0.000)**
OLS estimation
F (zero slopes)=17.05 (P-value =0.000**)
N=1530, adj- 2R =0.068 * Siginificant at 5 %, ** Significant at 1 %.
With this estimation, we have a result as follows:
[Result 7] There is a significant positive correlation between the âexit variableâ and the âindividual
payoff in a round.â We have the data for âindividual payoff in a roundâ after the decision making on the
exit option (Figure 1), we have the result that there is a positive effect of the âexitâ on the âindividual
payoff in a round.â
As there are interesting results concerning the control variables, we summarize them as follows:
142
[Result 8] There is a significant negative correlation between the âgroup sizeâ and the âindividual payoff
in a round.â The group size is determined before the âindividual payoff in a roundâ is determined, we
have the result that there is a negative effect of the âgroup sizeâ on the âindividual payoff in a round.â
In Model IV, we examine the effect of the exit on the âgroup size.â The result of the estimation is
shown in Table 4.
Table 4: Effect on the âgroup sizeâ
Dependent Variable: Group Size Variables Coefficients (P-value)
Constant Term Exit Variable Dummy for 50 yen moving cost Dummy for 0 yen moving cost Trend
5.500 (0.000)** -0.058 (0.620) -0.042 (0.711)
0.671 (0.000)** -0.068 (0.001)**
OLS estimation
F (zero slopes)=9.898 (P-value =0.000**)
N=1530, adj- 2R =0.022 * Siginificant at 5 %, ** Significant at 1 %.
With this estimation, we have a result as follows:
[Result 9] There is not a significant correlation between the âexit variableâ and the âgroup size.â
4. Conclusion
We investigate the effect of the exit on various variables: the group surrounding cooperation rate, the
individual cooperation rate, the individual payoff, and the group size. We derive several conclusions.
Firstly, the participants succeeded in moving to the more cooperative groups (Result 1). Though the
exit itself does not affect the participantsâ cooperative behaviors (Result 4), the individual cooperation
rates and the group surrounding cooperation affected each other positively (Result 2, 5). We can conclude
that the exit option made the group more cooperative. This positive effect is detected in terms of the
payoffs (Result 7). In other words, the positive effect of the exit choice dominates the negative effect of
the exiting in the experimental data. However, the gain of the exit is 0.77 yen per exiting. As it is below
the costs of the exit, 20 yen or 50 yen, the net gain from the exit choice is negative values.
Secondly, we confirm the negative effect of the group size on the cooperation rate, that is, if the
group size grows, the rate of cooperation decreases (Result 3, 6). These results are consistent with the
results in Kobayashi et al [2005] included in this volume and former works (Kollock [1998], Ehrhart and
143
Keser [1999]). However, we do not find the effect of the exit choice on the group size. One of the reasons
is that there are a few explanatory variables.
References Dawes, Robyn M, Richard H. Thaler 1988. âAnomalies: Cooperationâ Journal of Economic Perspectives 2 187-197.
Ehrhart, Karl-Martin and Claudia Keser. 1999. âMobility and Cooperation: On the Run.â CIRANO Working Papers
99s-24.
Fujiyama, Hideki, Jun Kobayashi, Yuhsuke Koyama, Hirokuni Oura. 2005a. âDecisions on the Exit: Micro analyses
of a Social Dilemma Experiment with Intergroup Mobility 1.â in this volume.
Fujiyama, Hideki, Jun Kobayashi, Yuhsuke Koyama, Hirokuni Oura. 2005b. âIntentions in the Exit: Micro analyses
of a Social Dilemma Experiment with Intergroup Mobility 3.â in this volume.
Kobayashi, Jun, Yuhsuke Koyama, Hideki Fujiyama, Hirokuni Oura, 2005 âRise and Fall of Cooperation: Macro
analyses of a Social Dilemma Experiment with Intergroup Mobility.â in this volume.
Kollock, Peter. 1998. âSocial Dilemmas: The Anatomy of Cooperation. Annual Review of Sociology 24:183-214.
Olson, Mancur. 1965. The Logic of Collective Action: Public Goods and the Theory of Groups. Harvard University
Press.
Orbell, John M. and Robyn M. Dawes. 1993. âSocial Welfare, Cooperatorsâ Advantage, and the Option of Not
Playing the Game.â American Sociological Review 58, 787-800.
Acknowledgement: Authors thank Hideki Ishihara, Kazuhiro Kagoya, Masayuki Kanai, Hideki Kamiyama, Naoko Taniguchi, Ryuhei Tsuji, Motoko Harihara, and Masayoshi Muto for their comments and support.
144
Intentions in the Exit Micro Analyses of a Social Dilemma Experiment with
Intergroup Mobility 3
Hideki Fujiyama, Jun Kobayashi, Yuhsuke Koyama, and Hirokuni Oura (Dokkyo University) (University of Chicago) (Tokyo Institute of Technology)
(Teikyo University)
Abstract: We investigate the intensions of exit choices in terms of predicted payoffs and predicted group sizes. As for the
predicted payoffs, non-cooperators usually try to move into groups with higher predicted payoffs. As for the
predicted group sizes, non-cooperators usually try to move into larger groups. Cooperators, on the other hand,
generally try to move into smaller groups. These facts are consistent with the interpretation that
non-cooperators try to enjoy free riding and cooperators try to escape from free riding.
Keywords exit, intention, social dilemma, mobility, experiment.
1. Introduction
Cooperators tend to exit from groups more than non-cooperators, on the other hand, non-cooperators are
more sensitive to the cooperation around them (Fujiyama et al [2005]). One reason for these facts is that
the cooperators escape from free riders and create a new desirable groups, on the other hand, the
non-cooperators move to enjoy free riding (Fujiyama et al [2005] and Erhart and Keser [1999]).
These results show the different exit behaviors between in the cooperators and in the non-cooperators.
However, it is important to note that, as there are many factors in the experiment, there is a possibility that
the intention of the participants is not clear in usual estimations. In addition, in order to construct the
institutions to promote cooperation in a group, it is a critical factor to note the different intentions on the
exit choices between in the cooperators and in the non-cooperators. Therefore, we compare the data for
the group to which participants moved actually with the data for the group to which participants can move
to potentially. With this comparison, we investigate the intentions on the exit choices.
In Section 2, we outline the data set. Section 3 reports the result and Section 4 concludes the paper. 2. Research design
2.1 The Experiment
This subsection is the same as the subsection 2.1 in Fujiyama et al [2005], which is included in this
volume. See the corresponding subsection.
145
2.2 Data and Estimation
Data
There are ten rounds in a session in which 17 participants are included. In each round, there are three
groups for which a participant can exit choice.9 The sample size is 5100 (= 3 groups Ã10 rounds Ã17 participants Ã10 sessions). There are data for an average payoff and a size for each group. This realized
values in a current round are information that is used for the decision on the exit. As it is difficult to
predict the average payoffs and the sizes of other groups in the next round, we assume that the participants
simply consider that realized values in a current round affect the payoff in the next round significantly,
that is, these data in the current round is interpreted as simple predicted values for each group in the next
round. These simple âpredicted value (payoff or group size)â are dependent variables.
We construct an âexit dummy variableâ, that is, if the group in the current round is the group to
which the player moves actually in the exit option in the current round, then the value is 1, otherwise, it is
0. Using this dummy variable, we divide all data into two categories. In the first category, the values of
the âexit dummy variablesâ are 0. In other words, the data in this category is the data for the group to
which participants can move potentially. If players select the group randomly in the exit choice,
characters of groups in this category were realized10. We use the results in this first category as criteria to compare. In the second category, the values of the âexit dummy variablesâ are 1. The data in this category
is the data for the group to which participants moved actually. This date include the intention in the exit
option because (1) this data is information that is used for the decision-making and (2) actually, the
participant moved to the group in this category. If there are some different results between in the first
category and in the second category, the intention of the exit choice is included.
An explanatory variable is an âindividual cooperation rate,â which is a cooperation rate of a
concerned participant in all 50 decisions. We make a comment on causality. As the âsimple predicted
valuesâ are values in groups to which the concerned player does not belong, there is no direct causality
from the âsimple predicted valuesâ to the âindividual cooperation rate,â that is, there is no reverse
causality.
The way to collect data is summarized in Figure 1.
9 In the last round, players cannot exit. However, data of the last round also have information for the criterion with
which we judge the bias of the result in the group to which the players move actually. Therefore we use the data for
the last round.
10 Of course, in exact analysis for random choices, we have to include the data in second category. However, the
total number of data in the first category is much larger than that in the second category. Therefore, the difference is
very small.
146
Figure 1: data set
Estimations
We consider two models in which dependent variables differ. In the first model (Model I), the âsimple
predicted payoffâ is a dependent variable. In the second model (Model II), the âsimple predicted group
sizeâ is a dependent variable. In both models, the âindividual cooperation rateâ is an explanatory variable.
Using the âexit dummy variable,â we examine the changes of constant term and coefficient of the
âindividual cooperation rate. In order to control the environment, we consider dummy variables for
50-yen-cost and 0-yen-cost conditions and seven dummy variables for sessions.11
3. Results
In Model I, we examine the difference in the âpredicted payoffs â among players with various âindividual
cooperation rates.â
First, we confirm the significant difference between the âpredicted payoffsâ in the first category in
which there are groups to which participants could move potentially and those in the second category in
11 With these 9 dummy variables, we can classify effects of each session completely.
group A group Dgroup Cgroup B
Individual Cooperation Realized Values Exit Dummy
Rate of Concerned Player in Other Groups Variable
Fixed value for the player Values in group A 0
Fixed value for the player Values in group B 0
Fixed value for the player Values in group D 0
Fixed value for the player Values in group A 0
Fixed value for the player Values in group B 1
Fixed value for the player Values in group D 0
concerned player
simple prediction D=1
147
which there are groups to which participants moved actually. Concerning the constant term and the
coefficient of the âindividual cooperation rates,â we have the significant difference between in the first
category and in the second category with a level of 1 % significance.12 Second, we estimate parameters in Model I. The result is shown in Table 1.
Table 1: Predicted payoffs
Dependent Variable: Predicted Payoffs (PP) Variables Coefficient (P-value)
Constant Term Exit Dummy for Constant Term Individual Cooperation Rate (ICR) Exit Dummy for the coefficient of ICR Dummy for 0 yen moving cost Dummy for 50 yen moving cost Dummy for session 1 with 50 yen moving cost Dummy for session 2 with 20 yen moving cost Dummy for session 3 with 0 yen moving cost Dummy for session 4 with 50 yen moving cost Dummy for session 5 with 50 yen moving cost Dummy for session 6 with 20 yen moving cost Dummy for session 7 with 20 yen moving cost
25.70 (0.000)** 3.463 (0.000)**
-1.284 (0.000)** -4.400 (0.000)**
-0.476 (0.076) 1.223 (0.000)**
-0.626 (0.019)* 0.585 (0.029)* 1.615 (0.000)**
-1.106 (0.000)** -2.114 (0.000)**
-0.447 (0.095) 2.444 (0.000)**
OLS estimation
F(zero slopes) =29.465 (P-value =0.000**)
N=5100, adj- 2R =0.062 * Significant at 5%, ** Significant at 1%
With this estimation, we have results as follows:
[Result 1] The âexit dummy variableâ for the constant term is significant and positive.
[Result 2] The coefficient of the âexit dummy variableâ for the âindividual cooperation rateâ is significant
and negative.
In Model II, we examine the difference in the âpredicted group size â among players with various
âindividual cooperation rates.â
First, we confirm the significant difference between the âpredicted group sizeâ in the first category
and those in the second category. Concerning the constant term and the coefficient of the âindividual
cooperation rates,â we have the significant difference between in the first category and in the second
category with a level of 1 % significance.13
12 Using the F test, the test statistic is 57.86 and the P-value is 0.000.
13 Using the F test, the test statistic is 7.818 and the P-value is 0.000.
148
Second, we estimate parameters in Model II. The result is shown in Table 2.
Table 2: Predicted group sizes
Dependent Variable: Predicted Group Sizes (PGS) Variables Coefficient (P-value)
Constant Term Exit Dummy for Constant Term Individual Cooperation Rate (ICR) Exit Dummy for the coefficient of ICR Dummy for 0 yen moving cost Dummy for 50 yen moving cost Dummy for session 1 with 50 yen moving cost Dummy for session 2 with 20 yen moving cost Dummy for session 3 with 0 yen moving cost Dummy for session 4 with 50 yen moving cost Dummy for session 5 with 50 yen moving cost Dummy for session 6 with 20 yen moving cost Dummy for session 7 with 20 yen moving cost
3.789 (0.000)** 0.525 (0.002)** 0.454 (0.001)**
-1.645 (0.000)** -0.003 (0.977) 0.152 (0.195) -0.362 (0.002)** 0.137 (0.241)
-0.303 (0.011)* 0.041 (0.726) -0.031 (0.791)**
-0.033 (0.778) 0.027 (0.812)
OLS estimation
F(zero slopes) = 4.137 (P-value =0.000**)
N=5100, adj- 2R =0.007 * Significant at 5%, ** Significant at 1%
With this estimation, we have results as follows:
[Result 3] The âexit dummy variableâ for the constant term is significant and positive.
[Result 4] The coefficient of âexit dummy variableâ for the âindividual cooperation rateâ is significant
and negative. On the other hand, the coefficient of the âindividual cooperation rateâ is significant and
positive.
To see the difference more clearly, we draws graphs of the estimated functions in Model I and Model
II (Figure 2, 3).14
14 In the graphs, we omit the common control variables, that is, we consider only the constant term, the âindividual
cooperation rateâ and the corresponding dummy variables.
149
0.2 0.4 0.6 0.8 1ICR
25
26
27
28
29
PP
Realization
Criterion
PP: Predicted Payoffs, ICR: Individual Cooperation Rate
Criterion: The line that is realized if the participants exit randomly.
Realization: The line that is realized with an actual exiting.
Figure 2: Predicted payoffs and Individual cooperation rate
The lower the participants have the âindividual cooperation rates,â the higher group they try to move into.
At the highest âindividual cooperation rate,â that is, it is near 1, the participants try to move into the group
with the lower payoff than the average âpredicted payoffsâ that would be realized with the random exits.
0.2 0.4 0.6 0.8 1ICR
3.2
3.4
3.6
3.8
4.2
PGS
Realization
Criterion
PGS: Predicted Group Sizes, ICR: Individual Cooperation Rate
Criterion: The line that is realized if the participants exit randomly.
Realization: The line that is realized with an actual exiting.
Figure 3: Predicted group sizes and Individual cooperation rate
The participants with the lower âindividual cooperation rateâ moves into the group whose size is larger
150
than the average size of groups that would be realized with the random exits. On the other hand, the
participants with the higher âindividual cooperation rateâ moves into the group whose size is smaller than
the average size of groups that would be realized with the random exits.
4. Conclusion
We investigate the intensions of the exit choices in terms of the predicted payoffs and the predicted group
sizes.
As for the predicted payoffs, the non-cooperators try to move into the groups with higher predicted
payoffs (Result 1, 2 and Figure 2). This is consistent with the results of Fujiyama et al [2005], that is, the
non-cooperators is sensitive to the cooperation rate around them and move to enjoy free-riding. On the
other hand, for cooperators, there is not a clear intention to the move into the group with the higher payoff
(Result 1, 2 and Figure 2).
As for the predicted group sizes, the non-cooperators try to move into the larger groups (Result 3, 4
and Figure 3). As the group size affects the cooperation rate negatively (Kobayashi et al [2005]), the larger
group is not desirable for free riding. However, in a larger group, the free riding is not standing out than in
a small group. This is one reason for this tendency.
The cooperators try to move into the smaller groups (Result 3, 4 and Figure 3). This is consistent
with result in Ehrhart and Keser[1999], that is, the cooperator tends to move into the smaller groups. In
addition, Ehrhat and Keser[1999] concludes that the cooperator escape from free riders and create new
groups. Though, in our experimental design, the number of groups is fixed and there is no choice to create
new groups,15 one reason for moving into smaller groups in our experiment is the same as the Ehrhat and Keser[1999]âs conclusion. From this viewpoint, we can understand why the cooperators moved to the
groups with lower payoffs, that is, the cooperators consider that free riders exit from the group with the
lower payoff and that if they, the cooperators, move into the group with the lower payoff, then they can
escape from the free riders.
As for future topics, there are low values of the R-squared, especially in the Model II. As there are
various intentions in the exit choice, we have to add some explanatory variables.
References Ehrhart, Karl-Martin and Claudia Keser. 1999. âMobility and Cooperation: On the Run.â CIRANO Working Papers
99s-24.
Fujiyama, Hideki, Jun Kobayashi, Yuhsuke Koyama, Hirokuni Oura. 2005. âDecision on the Exit: Micro analyses of
a Social Dilemma Experiment with Intergroup Mobility 1.â in this volume.
15 Within four groups, an empty group can exist. If there is an empty group, any participants can move into the
empty group.
151
Acknowledgement: Authors thank Hideki Ishihara, Kazuhiro Kagoya, Masayuki Kanai, Hideki Kamiyama, Naoko Taniguchi, Ryuhei Tsuji, Motoko Harihara, and Masayoshi Muto for their comments and support.
152
Decisions on Cooperation Micro Analyses of a Social Dilemma Experiment with
Intergroup Mobility 4
Hideki Fujiyama (Dokkyo University)
Abstract: We estimate individual participantâs behavior patterns using experimental data from ârepeated social dilemma
games.â Various cooperation behaviors are studied in theoretical analysis. The purpose of this paper is to
provide empirical facts for the analysis. The results are as follows: The cooperation behaviors are classified
into six categories. Especially, we found both the "conditional cooperators" who cooperate with others if others
also cooperate with them and the "empirical players" who choose their actions based on their past actions.
These behaviors are most apparent in the social dilemma game with a restricted exit options.
Keywords: cooperation, decision-making, social dilemma, mobility, experiment.
1. Introduction
In the evolutionary game theory, there are various behavior patterns at the individual level. However, we
have not much information for the actual behaviors of individuals in social dilemma games, though there
are some works to investigate the behaviors (Camerer [2003]). It is important, for the further analysis to
tackle the âsocial dilemmaâ problems especially in designing institutions, to gather facts concerning the
actual behaviors instead of the theoretical ones.
In the âsocial dilemmaâ games, Perez-Marti and Tomas [2004] tests the three different behavior
patterns: the standard Bayesian model, the Regret model in which the payoff differences between
contributing and not contributing is taken account for, and Warm-grow model in which the satisfaction
that comes from contribution is taken account for. Under the analysis in Perez-Marti and Tomas [2004],
there is an implicit assumption that all participants in the experiment use the same behavior pattern.
However, this assumption is not consistent the assumption of evolutionary game theory in which there are
many different behaviors simultaneously. In addition, it is natural that we behave differently in a real life.
Fischbcher et al [2001] estimates different behavior patterns by the individual. In 44 participants, there are
four different behavior patterns: âConditional cooperatorsâ who, roughly speaking, are want to contribute
if others also want to contribute. âFree ridersâ who are do not contribute at all, âHump shaped
contributorsâ who, roughly speaking, is âconditional cooperatorsâ at the low contributing level, but reduce
their contribution beyond the some contributing level, and âOther patterns.â In their woks, there is no
repetition of games and the participants describe only behavior schedules. It is important to note that, in
153
principle, describing the schedule in mind and using the schedule repeatedly in actual games are different
things. As there is no guarantee for using the schedule, information based on actual data is more
important.
The distinguish feature of this paper is as follows: we estimate the behavior patterns by the actual
data in ârepeated social dilemma games.â In addition to this, we examine the effect of mobility on the
behavior patterns, too.
In Section 2, we outline the data set. Section 3 reports the results and concludes the paper. 2. Research design
2.1 The Experiment
This subsection is the same as the subsection 2.1 in Fujiyama et al [2005], which is included in this
volume. See the corresponding subsection.
2.2 Estimation
Data
As there are ten rounds in which there are 5 stages, each participant has 50 decision-makings on
âcooperationâ (voluntary contribution to the group), or not. We construct a âvariable on cooperation,â
that is, if a participant chooses the option of cooperation then the value is 1, otherwise, it is 0. This binary
variable is a dependent variable.
As for target explanatory variables, we consider two variables. First, we consider a âgroup
surrounding cooperation rate, â which is a groupâs average cooperation rate excluding the concerned
participant in that round. For example, there are four participants in a group and the cooperation rate of
Participant 1 is 0.4; the cooperation rate of Participant 2 is 0.6; the cooperation rate of Participant 3 is 0.2;
and the cooperation rate of Participant 4 is 0.3. For Participant 2, the âgroup surrounding cooperation
rateâ is 0.3 (=(0.4+0.2+0.3)/3). Second, we consider a âprevious action, â which is a choice that the
concerned participant took actually in the previous stage, that is, â 1âAction â in the notation of the
regression model.
There are two control variables. First, we consider the âgroup size, â which is the total number of
participants in a group in the current round.16 Second, we consider a dummy variable for the first stage,
16 The âgroup sizeâ is determined at the beginning of the round, and all participants know this information in the
first stage in a round. Therefore, we use the âgroup sizeâ in current round not in the previous round.
154
as there is a tendency of a high cooperation rate.17 As for the multicollinearity, we examine the stability of estimated parameters. In order to examine
the stability, we add the lagged variables for the action to the estimation model, that is, we sequentially
add the second lagged value for the action, â 2âAction â, the third lagged value for the action,
â 3âAction â and so on. We add the sixth lagged variables in the maximal cases.18 We judge that the
estimated parameters are stable, if there are no qualitative differences in at least three different regression
models. In addition, we have the correlation coefficients among the explanatory variables and find that all
values are less than 0.5 except for several cases. In all exceptional cases, the values are about 0.6. We
have the VIFs and find that all values are less than 1.6 except for several cases. In all exceptional cases,
the values are about 2. In all exceptional cases, the âstability criterionâ mentioned above is satisfied.
The significance levels for the LR-test (zero slope) and t-test are 5 %. As the dependent variable (the
âvariable on cooperationâ) is binary data, we use Probit and Logit models to estimate parameters.
Classes
We consider six classes for the behavior patterns of participants: (1) If a coefficient of the âgroup
surrounding cooperation rateâ is positive and significant, then we call the participant a âconditional
cooperator.â (2) If a coefficient of the âprevious actionâ is significant and positive, then we call the
participant an âempirical player.â19 (3) If a coefficient of the âprevious actionâ is significant and negative, then we call the participant a âtry and error player.â(4) If a participant chooses the choice of
cooperation more than 41 times, then we call the participant a âcooperator.â (5) If a participant chooses
the choice of non-cooperation more than 41 times, then we call the participant a ânon-cooperator.â20 (6) If the behavior of the participant is not included in all classes mentioned above, then we call the
participant âothers.â
17 As the mean mobility rate is about 0.33, that is, the ratio of new members is low in the first stage in a new round,
we assume that the âgroup surrounding cooperation rateâ in the last stage in the previous round is relevant
information for the cooperation decision making in the first stage in the new current round. There is another
assumption that the cooperation decision-makings in the first stage in a round is qualitatively different from those in
other stages. Given this assumption, we should omit the data in the first stage. This is a future topic for our analysis.
18 We use the higher lagged variables, 2âAction , âŠ, 6âAction , only for judging the stability. As for the target
explanatory variable, we examine the significance for the 1âAction only. The reason is that (1) it is difficult to
interpret the higher significant lagged variables, especially in the case that the 1âAction is not significant but the
other higher lagged variables are significant, and (2) classifying 234 estimations into some categories needs a
simplification for procedures.
19 There is a certain reinforcement learning process implicitly behind this behavior.
20 In Ehrhart and Keser [1999], if a participant chooses the choice of cooperation (or non -cooperation) more than
half, they call the participant a âcooperator (or non- cooperator).â Therefore, our criterion is a stricter criterion than
the Ehrhart and Keser [1999]âs criterion.
155
3. Results and Conclusion
The results of the estimations are summarized in Figure 1. All results are in the Appendix.
We find the various significant cooperation behaviors. The group surrounding cooperation rates and
the previous action are important factors.
Comparing Fischbacher et al [2001], the percentage of âfree ridingâ is very close, as the percentage
is 29.5 % in Fischbacher et al [2001], on the other hand, that in our analysis is 28 .2%.21 The percentage of âconditional cooperationâ is different, as the percentage is 50.0 % in Fischbacher et al [2001], on the
other hand, that in our analysis is about 11 .9%.22 The reason for this is as follows: As, in Fischbacher et al [2001], the game is played once, and only the âcontribution schedulesâ are submitted, on the other hand,
in our analysis, the game is repeated and the behavior patterns is estimated by the actual actions, the
behavior patterns tends to simplified in Fischbacher et al [2001] than in our analysis.
In Appendix, the significant behaviors become obvious in the 20-yen-cost âSession 7â in which there
are 10 âconditional cooperatorsâ and 3 âempirical playersâ and the 50-yen-cost âSession 2â in which there
are 5 âconditional cooperatorsâ and one âempirical player.â In addition to this, the âconditional
cooperatorsâ and âempirical playersâ become obvious in the 50-yen-cost and 20-yen-cost condition than
in the no-mobility and 0-yen-cost condition, that is, 22.7 % of the participants are the âconditional
cooperatorsâ or the âempirical playersâ in the 50-yen-cost and 20-yen-cost condition, on the other hand,
8.1 % in the no-mobility and 0-yen-cost condition.
One reason for this is as follows: As there is a high mean mobility rate (67.3 %) in 0-yen-cost
condition, the participants feel that the game is played with all 17 participants within one group as same as
the case in the no-mobility conditions in which the group is fixed. In other words, the effect of selecting
the members decreases in 0-yen-cost condition, and the situation become similar to that in the no-mobility
condition. This ineffectiveness of the selecting members diminishes the incentive for using strategic
behaviors.
It is a future topic to investigate the condition under which the desirable behavior patterns are
realized and high cooperation rate is attained.
21 In Fischbacher et al [2001], the participants are asked to âindicate for each average contribution level of other
group members how much they want to contribute to the public good.â The behaviors are classified depending on this
contribution schedule. If the participants submitted a contribution schedule that contained â0â for every average
contribution level of other group members, they are called âfree riders.â
22 In Fischbacher et al [2001], if there is significant and positive Spearman rank correlation coefficient between
âaverage contribution level of other groupâ and own contribution in the âcontribution schedule,â the participant is
called a âconditional cooperator.â
156
(Percentage in Parentheses)
Figure 1: Classification
234 Players
8
115 23
1
4 11
6 (0.004)
(0.017)
(0.098)
(0.034)
(0.491)
(0.025)
(0.047)
Cooperators
Try & Error
Empirical Players
Conditional Cooperators
Others
Non-Cooperators
66 (0.282)
157
Appendix 50-Yen-Costs Sessions:
CC: Conditional Cooperators EP: Empirical Players T&E: Try and Error
NC: Non-Cooperators Co : Cooperators Oths : Others
Session 1 CC EP T&E NC Co Oths Session 2 CC EP T&E NC Co Oths
player 1 1 player 1 1
player 2 1 player 2 1
player 3 1 player 3 1
player 4 1 player 4 1
player 5 1 player 5 1
player 6 1 player 6 1
player 7 1 player 7 1
player 8 1 player 8 1
player 9 1 player 9 1
player 10 1 player 10 1
player 11 1 player 11 1
player 12 1 player 12 1
player 13 1 player 13 1
player 14 1 player 14 1
player 15 1 player 15 1
player 16 1 player 16 1
player 17 1 player 17 1
sum. 1 0 0 4 0 12 sum. 5 1 0 3 0 8
Session 3 CC EP T&E NC Co Oths Session 4 CC EP T&E NC Co Oths
player 1 1 player 1 1
player 2 1 player 2 1
player 3 1 player 3 1
player 4 1 player 4 1
player 5 1 player 5 1
player 6 1 player 6 1
player 7 1 player 7 1
player 8 1 player 8 1
player 9 1 player 9 1
player 10 1 player 10 1
player 11 1 player 11 1
player 12 1 player 12 1
player 13 1 player 13 1
player 14 1 player 14 1
player 15 1 player 15 1
player 16 1 player 16 1
player 17 1 player 17 1
sum. 0 2 0 9 0 6 sum. 0 2 0 6 0 9
158
20-Yen-Costs Sessions:
CC: Conditional Cooperators EP: Empirical Players T&E: Try and Error
NC: Non-Cooperators Co : Cooperators Oths : Others
Session 5 CC EP T&E NC Co Oths Session 6 CC EP T&E NC Co Oths
player 1 1 player 1 1 1
player 2 1 player 2 1
player 3 1 player 3 1
player 4 1 player 4 1
player 5 1 player 5 1
player 6 1 player 6 1
player 7 1 player 7 1
player 8 1 player 8 1
player 9 1 player 9 1
player 10 1 player 10 1
player 11 1 player 11 1
player 12 1 player 12 1
player 13 1 player 13 1
player 14 1 player 14 1
player 15 1 player 15 1
player 16 1 player 16 1
player 17 1 player 17 1
sum. 2 1 1 6 0 7 sum. 3 1 0 6 1 7
Session 7 CC EP T&E NC Co Oths Session 8 CC EP T&E NC Co Oths
player 1 1 player 1 1 1
player 2 1 player 2 1
player 3 1 1 player 3 1
player 4 1 player 4 1
player 5 1 player 5 1
player 6 1 1 player 6 1
player 7 1 player 7 1
player 8 1 1 player 8 1
player 9 1 player 9 1
player 10 1 player 10 1
player 11 1 player 11 1
player 12 1 player 12 1
player 13 1 player 13 1
player 14 1 player 14 1
player 15 1 player 15 1
player 16 1 player 16 1
player 17 1 player 17 1
sum. 10 3 1 4 1 1 sum. 2 2 2 5 0 7
159
0-Yen-Cost Sessions:
CC: Conditional Cooperators EP: Empirical Players T&E: Try and Error
NC: Non-Cooperators Co : Cooperators Oths : Others
Session 9 CC EP T&E NC Co Oths Session 10 CC EP T&E NC Co Oths
player 1 1 player 1 1
player 2 1 player 2 1
player 3 1 player 3 1
player 4 1 player 4 1
player 5 1 player 5 1
player 6 1 player 6 1
player 7 1 player 7 1
player 8 1 player 8 1
player 9 1 player 9 1
player 10 1 player 10 1
player 11 1 player 11 1
player 12 1 player 12 1
player 13 1 player 13 1
player 14 1 player 14 1
player 15 1 player 15 1
player 16 1 player 16 1
player 17 1 player 17 1
sum. 0 0 0 7 1 9 sum. 2 0 0 3 0 12
160
No-moving Sessions:
CC: Conditional Cooperators EP: Empirical Players T&E: Try and Error
NC: Non-Cooperators Co : Cooperators Oths : Others
Session 11 CC EP T&E NC Co Oths Session 12 CC EP T&E NC Co Oths
player 1 1 player 1 1
player 2 1 player 2 1
player 3 1 player 3 1
player 4 1 player 4 1
player 5 1 player 5 1
player 6 1 player 6 1
player 7 1 player 7 1
player 8 1 player 8 1
player 9 1 player 9 1
player 10 1 player 10 1
player 11 1 player 11 1
player 12 1 player 12 1
player 13 1 player 13 1
player 14 1 player 14 1
player 15 1 player 15 1
player 16 1 player 16 1
sum. 0 2 0 6 2 6 sum. 2 0 1 3 0 10
Session 13 CC EP T&E NC Co Oths Session 14 CC EP T&E NC Co Oths
player 1 1 player 1 1
player 2 1 player 2 1
player 3 1 player 3 1
player 4 1 player 4 1
player 5 1 player 5 1
player 6 1 player 6 1
player 7 1 player 7 1
player 8 1 player 8 1
player 9 1 player 9 1
player 10 1 player 10 1
player 11 1 player 11 1
player 12 1 player 12 1
player 13 1 player 13 1
player 14 1 player 14 1
player 15 1 player 15 1
player 16 1 player 16 1
sum. 1 1 1 2 0 11 sum. 0 0 1 2 3 10
161
References Camerer, Coline f. 2003 Behavioral Game Theory: Experiments in Strategic Interaction. Princeton University Press.
Ehrhart, Karl-Martin and Claudia Keser. 1999. âMobility and Cooperation: On the Run.â CIRANO Working Papers
99s-24.
Fischbacher, Urs, Simon Gachter, Ernst Fehr. 2001. âAre people conditionally cooperative? Evidence from a public
goods experiment.â Economics letters 71 397-404.
Fujiyama, Hideki, Jun Kobayashi, Yuhsuke Koyama, Hirokuni Oura. 2005. âDecisions on the Exit: Micro analyses of
a Social Dilemma Experiment with Intergroup Mobility 1.â in this volume.
Perez-Marti, Felipe, Josefa Tomas. 2004. âRegret, Warm-glow and Bounded Rationality in Experiments on Binary
Public Goodsâ Journal of Economic Behavior & Organization 55 343-353. Acknowledgement: Authors thank Hideki Ishihara, Kazuhiro Kagoya, Masayuki Kanai, Hideki Kamiyama, Naoko Taniguchi, Ryuhei Tsuji, Motoko Harihara, and Masayoshi Muto for their comments and support.
162
Effects of Unanimity on Cooperation Micro Analyses of a Social Dilemma Experiment with
Intergroup Mobility 5
Hideki Fujiyama Hirokuni Oura (Dokkyo University) (Teikyo University)
Abstract: We examine the relationship between non-random sequences of cooperation choices and unanimous
cooperation in a group. We find that unanimous cooperation generally affects cooperation behavior positively.
This positive effect is most prominent in moderate mobility conditions. This fact implies that unanimous
cooperation is a signal for cooperators in a group and the signal is clearer in moderate exit costs conditions than
in no-mobility and high mobility conditions.
Keywords: cooperation, unanimity, social dilemma, run, experiment.
1. Introduction
For solving the social dilemma problem, there are two streams: strategic solutions and motivation
solutions (Kollock [1998]).23 In the stream of the strategic solutions, egoistic players are assumed,
and the reciprocity and the choice of partners are important factors.24 On the other hand, in the stream of the motivation solutions, altruistic players are assumed, and it is known that the
communication and the group identity are important factors to promote this altruism.
In this paper, we look for the phenomenon that promotes the cooperation in an experiment in the
stream of the motivation solutions.
In the experimental data, there is a cluster of cooperation both in the time series data and in the
cross section data. More concretely, we can find the sequence of cooperation choices in a player. On
the other hand, there is a group in which all players choose the choices of cooperation simultaneously.
We examine the relationship between these phenomena using the cross table analysis.
In Section 2, we outline the data set. Section 3 reports the results and Section 4 concludes the
paper.
23 If we consider the changes in the structure of the game, there is a structural solution in which the game is altered
in order to solve the social dilemma problem. In both strategic and motivation solutions, there is no changes in the
structure of the game (Kollock [1998]).
24 The exit option as a way of selecting the members in a group is examined in Fujiyama et al [2005a, b, c]. The
conditional cooperator is detected in Fujiyama [2005d]. These works are in the stream of strategic solutions.
163
2. Research design
2.1 The Experiment
The subsection is the same as the subsection 2.1 in Fujiyama et al [2005a], which is included in
this volume. See the corresponding subsection.
2.2 Methods
Data
As there are ten rounds in which there are 5 stages, a participant has 50 decision-makings on
âcooperationâ (voluntary contribution to the group). We construct a âvariable on cooperation,â that
is, if a participant chooses the option of cooperation then the value is 1, otherwise, it is 0. We
calculate an âindividual cooperation rate,â which is the ratio of cooperation in all 50 decisions.
This measure is used in a run test. As there are ten sessions in which 17 participants took part and
four sessions in which 16 participants took part, there are 234 participants to examine.
Criterion for a cross table
We consider two criterion for a cross table. First, we examine whether the participant continue to
choose the choice of cooperation significantly. We examine the length of run of cooperation in a
âvariable on cooperationâ given the âindividual cooperation rate.â For example, consider that there
are ten decisions and three players, A, B, C, whose âindividual cooperation rateâ are 0.4. In Figure 1,
we consider that Player C has a significant long run of cooperation because, if the decision-making is
random, the run of cooperation for Player C happens rarely. For this judgment, we use the tests based
on the length of the longest run.25 As the frequency of cooperation choices and the length of the longest cooperation run are obtained from the data in the experiment, we can have the test statistics.
As it is difficult to calculate the exact distribution function, we obtain it using a computer simulation
(Monte Carlo Analysis).26 The graph of the distribution function of the length of the longest cooperation run with 7 cooperation choices and 43 non-cooperation choices is shown in Figure 2. In
this case, the probability for the runs in which the length of the longest one is 1 is 0.3917; the
probability for 2 is 0.5286; the probability for 3 is 0.0718, and so forth. In this test, the null
hypothesis is that the runs are realized at random. If the runs that reject the null hypothesis are
detected, we think that there are some hidden factors that affect the participantâs behavior. As one of
reasonable candidates for these factors, we consider the following second criterion.
25 See Gibons and Chakraborti [1992] for a detailed explanation of the tests based on runs.
26 We derive the distribution functions with 100,000 times trials using Mathematica.
164
Figure 1: Runs of Cooperation
Probability
The length of the longest cooperation run Figure 2: Example: the distribution function
Second criterion is as follows: we examine whether the participant experienced the unanimity of
cooperation in a group, that is, all participants who belong to a group choose the choice of
cooperation in a game.
We examine the relationship between two criteria using the cross table analysis. As we control the
âindividual cooperation rateâ in the test based on the length of the longest run, these two criteria are
0.391
0.5286
0.0718
0.0075
0.0003 0.0001 0.0000
Player A Player B Player C
à â Ã
à à Ã
â Ã â
à â â
â Ã â
â Ã â
à à Ã
à â Ã
â Ã Ã
à â Ã
The length of the longest run: âïŒCooperation
2 1 4 ÃïŒNon-cooperation
Longest
Run
Longest
Run
165
independent for each other.
3. Results
As the distribution function is a discrete function, there are cases in which critical value and the
test statistic are in the same religion. In these cases, we cannot judge whether the test statistics are
larger than the critical value, or not. For example, in Figure 2, if we have the 5 % significant level,
the critical value is in 3 of the length. If a realized length of the longest cooperation run is also 3, we
cannot judge whether the test statistics (that is 3) is larger than the critical value, or not. Of course,
there is a way of thinking that, in this case, we consider that the null hypothesis is not rejected. But if
we accept this way of thinking, there is a bias not to reject the null hypothesis in this case. In other
words, in Figure 2, we do not test the hypothesis under the 5 % significant level but under 1 %
significant level substantially. In order to avoid this bias, we omit the samples of these cases from the
all data.27
The result is shown in Table 1. We find the positive association between two criteria.28 Table 1: Cross Table
Non-random sequence of cooperation choices Yes No Sum.
Yes 29 72 101 No 10 73 83
Unanimous Cooperation in a group Sum. 39 145 184 Cramerâs V =0.202, 2Ï =7.57 (p-value <0.01)
As for the samples in the 20-yen-cost and 50-yen-cost conditions, we find that the positive
association between two criteria is more outstanding.
27 Though we accept the way of thinking that we do not reject the null hypothesis, the results are not altered
qualitatively. The results are shown in Appendix.
28 The association (the Cramerâs V) is corresponding to the correlation coefficient. It seems that 0.202 is low.
However, it is important to note that the value of the Cramerâs V in the below case is also 0.2:
B1 B2 Sum. A1 60 40 100 A2 40 60 100 Sum . 100 100 200
The Cramerâs V in qualitative data tends to be lower than the correlation coefficient in the quantitative data. This
example is cited from Takahashi [1992, p.181-182].
166
Table 2: Cross Table (20 yen costs and 50 yen costs) Non-random sequence of cooperation choices Yes No Sum.
Yes 25 43 68 No 4 35 39
Unanimous Cooperation in a group Sum. 29 78 107 Cramerâs V =0.287, 2Ï =8.81 (p-value <0.01), Fisherâs exact probability testâs p-value <0.01
4. Conclusion
We examine the relationship between the non-random sequence of cooperation choices and the
unanimous cooperation in a group. We find a positive association between two criteria. In addition,
we find that the experience of the unanimous cooperation is realized in the early parts of the
cooperation run. We conclude that the unanimous cooperation affects the cooperation behavior
positively. In other words, it is a factor to promote the cooperation in a group.
This positive effect of unanimity is prominent in the 20-yen-cost and 50-yen-cost conditions. The
reason of this is as follows: In social dilemma game, it is important to guess othersâ behavior in a
group.29 From this viewpoint, the communication and the group identity can be interpreted as the way to bring the participants the good guess. The unanimous cooperation in a group is interpreted
similarly, if we consider the unanimous cooperation as a signal of high cooperation of others in a
group. This signal is weaken in a no-mobility condition as they interact repeatedly for a long time
and have much information except the unanimous cooperation. In 0-yen-cost conditions, this signal is
also weaken, as many participants move into the group. On the other hand, because, in the
20-yen-cost and 50-yen-cost conditions, the past information is a little and the noise with mobility is
also low, the signal is clearer than in the 0-yen-cost and no-mobility conditions.
As for the future topics, we examine the difference the 20-yen-cost and 50-yen-cost conditions and
the 0-yen-cost and no-mobility conditions using some statistical test. In addition, it is needed to
obtain the numerical information with which we know when the experience of the unanimous
cooperation is realized in the cooperation run.
29 Though the analysis is based on the trust game, we find the same comments in Bohnet and Croson [2004] and
Eckel and Wilson [2004].
167
Appendix
Table 3: Cross Table Non-random sequence of cooperation choices Yes No Sum.
Yes 29 84 113 No 10 111 121
Unanimous Cooperation in a group Sum. 39 195 234 Cramerâs V =0.233, 2Ï =12.7 (p-value <0.01)
Table 4: Cross Table (20 yen costs and 50 yen costs) Non-random sequence of cooperation choices Yes No Sum.
Yes 25 50 75 No 4 57 61
Unanimous Cooperation in a group Sum. 29 107 136 Cramerâs V =0.325, 2Ï =14.3 (p-value <0.01), Fisherâs exact probability testâs p-value <0.01
References Bohnet, Iris, Rachel Croson 2004 "Editorial Trust and Trustworthiness" Journal of Economic Behavior &
Organization 55 443-445.
Eckel, Catherine C., Rick K. Wilson 2004 "Is Trust a Risky Decision?" Journal of Economic Behavior &
Organization 55 447-465.
Fujiyama, Hideki, Jun Kobayashi, Yuhsuke Koyama, Hirokuni Oura. 2005a. âDecisions on the Exit: Micro analyses
of a Social Dilemma Experiment with Intergroup Mobility 1.â in this volume.
Fujiyama, Hideki, Jun Kobayashi, Yuhsuke Koyama, Hirokuni Oura. 2005b. âPerformance of the Exit: Micro
analyses of a Social Dilemma Experiment with Intergroup Mobility 2.â in this volume.
Fujiyama, Hideki, Jun Kobayashi, Yuhsuke Koyama, Hirokuni Oura. 2005c. âIntentions in the Exit: Micro analyses
of a Social Dilemma Experiment with Intergroup Mobility 3.â in this volume.
Fujiyama, Hideki, Jun Kobayashi, Yuhsuke Koyama, Hirokuni Oura. 2005d. âDecisions on Cooperation: Micro
analyses of a Social Dilemma Experiment with Intergroup Mobility 4.â in this volume.
Gibbons, Jean Dickinson Gibbons, Subhabrata Chakraborti 1992 Nonparmetric Statistical Inference (3rd ed.) 1992
Marcel Dekker Inc.
Kollock, Peter. 1998. âSocial Dilemmas: The Anatomy of Cooperation. Annual Review of Sociology 24:183-214.
Takahashi, Nobuo 1992 Keiei Toukei Nyuumon, Tokyo Daigaku Syuppankai (in Japanese). Acknowledgement: Authors thank Takashi Matsui for his comments on methods of tests. We also thank Jun Kobayashi, Hideki Ishihara, Kazuhiro Kagoya, Masayuki Kanai, Hideki Kamiyama, Naoko Taniguchi, Ryuhei Tsuji, Motoko Harihara, and Masayoshi Muto for their comments and support.
168
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ãæç®ã Cosmides, L. 1989. âThe logic of social exchange: Has natural selection shaped how humans reason? Studies with
the Wason selection taskâ Cognition, 31, 187-276
Davis,Morton D. 1970. Game Theory Charles.E. Tuttle Inc. Ltd. =æ¡è°·ç¶ã»æ£®å çŸ. 1973. ãã²ãŒã ã®
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Resolution vol.10 issue3:363-366 å¿ç°åºäžåž«. 2003. ãé²åã²ãŒã çè«ã¯æ°ç瀟äŒåŠã«å¿çšå¯èœãïŒããçè«ãšæ¹æ³ãvol.18 No.2 Taylor,M. 1987. The possibility of cooperation, New York: Cambridge University Press.=æŸåæ. 1995.
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Theoretical Placing of Playersâ Shifts in NPD Hideki Kamiyama
Hosei University
191
The purpose of this paper is placing players' shifts on the game theory. First, We confirm the necessity of
the iterated game theory and show the paradigm of âquasi-iterated gamesâ that is different from the paradigm
of regarding playersâ shifts as strategies. The quasi-iterated games in this case are mixtures of 50 times (10
rounds) iterated games and only 10 series of 5 times iterated games. Next, We show the results of experiments
and point out the possibility of the paradigm of quasi-iterated games for analysis of social acts.
192
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