ICSD2009
Kyoto
The effect of common knowledge
– Why do people cooperate more when they face
a social dilemma situation where mutual
cooperation yields restoration of fairness?
Nobuyuki Takahashi (Hokkaido University)
Ryoichi Onoda (Hokkaido University)
Hikaru Hamada (Hokkaido University)
Rie Mashima (Kumamoto Gakuen University)
E-mail: [email protected]
Introduction
There have been many collective behaviors in human history.
Collective behaviors seem to be thrived when the purpose
is the restoration of fairness (e.g., civil rights movements,
anti-Vietnam War movements).
Why?
Many collective behaviors involve social dilemmas.
So, isn’t free-riding still the better option than
participating in a social movement?
2
Takezawa (1999)
1) Experience of unfairness invokes the sense that unfairness
is shared among the other people.
2) The goal changes from pursuing self-interest to jointly
restoring fairness.
3) Expectation of others’ cooperation in one-shot public goods
game (PGG)
Provision of PG restores
Ordinary one-shot PGG
fairness
Since expectation of others’ cooperation promotes cooperation,
<
4) Cooperation rate
Ordinary one-shot PGG
<
Provision of PG restores
fairness
Why does the experience of unfairness
promote expectation of others’ cooperation?
3
Takezawa (1999)
According to Takezawa (1999)…
 The sense of fairness activates the common
knowledge that everybody was treated unfairly.
 This common knowledge induces higher level of
expectation that leads to higher level of
cooperation.
Taken for granted, but…
Why does this process occur?
Why is the expectation of others’ cooperation
higher when participants were all treated
unfairly?
4
What affects expectation?
Two reasons to defect in SD (e.g., Dawes et al. 1986; Van Lange et
al. 1992; Yamagishi & Sato 1986)
(1) Greed – the temptation to free-ride
(2) Fear – the prospect that one's cooperation may be
exploited


Not greed but fear affects expectation of others’
cooperation.
However, there can be at least two sources of fear.
Fear of greed
Fear of fear
What is the function of being treated unfairly?
5
Revisiting Takezawa (1999)
What is the function of being treated unfairly?
Two possibilities
(1) Reduction of fear of greed – People expect that the
experience of unfairness transforms the goal of other
people from maximizing self-interest to achieving
mutual cooperation in order to restore fairness.
We want to restore fairness!
The other people will cooperate
because they are no longer greedy.
6
Revisiting Takezawa (1999)
What is the function of being treated unfairly?
Two possibilities
(1) Reduction of fear of greed – People expect that the
experience of unfairness transforms the goal of other
people from maximizing self-interest to achieving
mutual cooperation in order to restore fairness.
However,
may
not be sufficient
Wethis
want
to restore
fairness! to induce
cooperation.
But the other people may still defect
because of fear.
Fear of fear
7
Revisiting Takezawa (1999)
(2) Reduction of fear of fear – Perception of
unfairness makes people expect that the other
people’s fear of greed was reduced.
The others are no longer greedy!
The other people will cooperate
because they have no fear.
Reducing fear of fear requires that the fact that everyone
was treated unfairly is a common knowledge.
8
Main purpose of the study
To differentiate these two functions and see if
reduction of fear of fear is necessary for
inducing higher level of cooperation
Reduction of fear of greed: Privately knowing that
everybody was treated unfairly is enough
Reduction of fear of fear: The fact that everybody
was treated unfairly must be a common knowledge
Manipulation:
Whether or not the fact that everybody was
treated unfairly is a common knowledge
9
Experiment
One factor, between-subjects design
Participants : 125 undergraduate students (M: 68, F: 56, UK: 1)
1) Control condition : Ordinary one-shot PGG without any
context
2) Common knowledge condition : One-shot PGG that
is identical with Control condition. However, before
playing the game, participants were all treated unfairly
by a dictator and they could restore fairness by
achieving mutual cooperation in PGG.
3) Private knowledge condition : The same as Common
knowledge condition. The only difference is that only
the participants knew that everybody was treated
unfairly by a dictator, and that they could restore
fairness by achieving mutual cooperation in PGG.
10
1) Control condition
Ordinary one-shot PGG without any context
1st stage: Social inference task (a bogus task)
 Each player was paid 500 yen ($5) for completing the
task.
500
yen
500
yen
500
yen
500
yen
500 Social
yen inference task
11
1) Control condition
Ordinary one-shot PGG without any context
2nd stage: One-shot step-level PGG
Cooperation : Provide 500 yen to the group
Defection : Keep 500 yen for oneself
500
yen
500
yen
500
yen
500
yen
500
yen
If more than 3 players cooperate,
12
1) Control condition
Ordinary one-shot PGG without any context
2nd stage: One-shot step-level PGG
Cooperation : Provide 500 yen to the group
Defection : Keep 500 yen for oneself
500
yen
4000 yen
If more than 3 players cooperate, a public good (4000 yen) is
provided.
13
1) Control condition
Ordinary one-shot PGG without any context
2nd stage: One-shot step-level PGG
Cooperation : Provide 500 yen to the group
Defection : Keep 500 yen for oneself
C
C
800
yen
C
800
yen
C
D
800
yen
500
yen
800
yen
800
yen
4000 yen
Total earnings of cooperators : 500-500+(4000/5)=800 yen
defectors : 500-0+(4000/5)=1300 yen
14
1) Control condition
Ordinary one-shot PGG without any context
2nd stage: One-shot step-level PGG
Cooperation : Provide 500 yen to the group
Defection : Keep 500 yen for oneself
500
yen
500
yen
500
yen
500
yen
500
yen
If less than 4 players cooperate,
15
1) Control condition
Ordinary one-shot PGG without any context
2nd stage: One-shot step-level PGG
Cooperation : Provide 500 yen to the group
Defection : Keep 500 yen for oneself
500
yen
500
yen
500
yen
0 yen
If less than 4 players cooperate, a public good is not provided.
16
1) Control condition
Ordinary one-shot PGG without any context
2nd stage: One-shot step-level PGG
Cooperation : Provide 500 yen to the group
Defection : Keep 500 yen for oneself
500
yen
500
yen
500
yen
Deception
0 yen
Although participants were told that there were
other participants and that they would interact with
them, actually each participant behaved as an
If less than 4 players cooperate, a public good is not provided.
individual. In other words, there was no real
interaction among the participants.
17
2) Common knowledge condition
Identical incentive structure with the one in the other 2
conditions
1st stage: Social inference task (a bogus task)
 As a 6-person group, players were paid 7000
yen ($70) for completing the task.
7000 yen
Social
inference task
18
2) Common knowledge condition
Identical incentive structure with the one in the other 2
conditions
 After 1st stage (before 2nd stage): Dictator game
A dictator was chosen randomly from the group and
decided to allocate 7000 yen among group members.
Recipient
?
yen
Recipient
Recipient
?
yen
?
yen
Recipient Recipient
?
yen
?
yen
Dictator
Participant
7000 yen
19
2) Common knowledge condition
Identical incentive structure with the one in the other 2
conditions
 After 1st stage (before 2nd stage): Dictator game
A dictator
wasdeception,
chosen randomly
from actually
the groupaand
Since
we used
however,
decided
allocate
yen among
members.
dictator
andtothe
other7000
recipients
did group
not exist.
Only
a participant was a real person. Also, dictator’s
decision was predetermined by the experimenter.
Recipient
?
yen
Recipient
Recipient
?
yen
?
yen
Recipient Recipient
?
yen
?
yen
Dictator
Participant
7000 yen
20
2) Common knowledge condition
Identical incentive structure with the one in the other 2
conditions
 After 1st stage (before 2nd stage): Dictator game
A dictator was chosen randomly from the group and
decided to allocate 7000 yen among group members.
The dictator allocated 4500 yen for himself and
500 yen for each of the other 5 players.
Recipient
500
yen
Recipient
Recipient
500
yen
500
yen
Recipient Recipient
500
yen
500
yen
Dictator
Participant
4500 yen
21
2) Common knowledge condition
Identical incentive structure with the one in the other 2
conditions
2nd stage: One-shot step-level PGG to restore fairness
 5 recipients were asked if they want to provide 500 yen.
Cooperation : Provide 500 yen to the group
Defection : Keep 500 yen for oneself
500
yen
500
yen
500
yen
500
yen
500
yen
Dictator
4500 yen
22
2) Common knowledge condition
Identical incentive structure with the one in the other 2
conditions
2nd stage: One-shot step-level PGG to restore fairness
500
yen
500
yen
C
C
C
500
yen
500
yen
C
D
500
yen
Dictator
If more than 3 recipients cooperate,
4500 yen
23
2) Common knowledge condition
Identical incentive structure with the one in the other 2
conditions
2nd stage: One-shot step-level PGG to restore fairness
C
C
C
C
D
500
yen
Dictator
If more than 3 recipients cooperate, 4000 yen was
forfeited from the dictator,
500 yen
4000 yen
24
2) Common knowledge condition
Identical incentive structure with the one in the other 2
conditions
2nd stage: One-shot step-level PGG to restore fairness
4000 yen
500
yen
Dictator
If more than 3 recipients cooperate, 4000 yen was
forfeited from the dictator, and recipients share
4000 yen equally.
500 yen
25
2) Common knowledge condition
Identical incentive structure with the one in the other 2
conditions
2nd stage: One-shot step-level PGG to restore fairness
Total earnings of cooperators : 500-500+(4000/5)=800 yen
defectors : 500-0+(4000/5)=1300 yen
C
C
800
yen
C
800
yen
C
800
yen
D
800
yen
500
yen
800
yen
Dictator
If more than 3 recipients cooperate, 4000 yen was
forfeited from the dictator, and recipients share
4000 yen equally.
500 yen
26
2) Common knowledge condition
Identical incentive structure with the one in the other 2
conditions
2nd stage: One-shot step-level PGG to restore fairness
D
D
500
yen
C
C
500
yen
D
500
yen
If less than 4 recipients cooperate, nothing
happens.
Total earnings of cooperators : 500-500=0 yen
defectors : 500-0=500 yen
Dictator
4500 yen
27
3) Private knowledge condition
Identical with Common knowledge condition
The only difference is that participants are the only one
who knew that everybody was treated unfairly.
After the dictator allocated 7000 yen, each player
received an allocation sheet that only says how much
she was allocated by the dictator.
Recipient
Recipient
Recipient
500
yen
?
yen
?
yen
Recipient Recipient
?
yen
?
yen
Dictator
? yen
28
3) Private knowledge condition
Identical with Common knowledge condition
The only difference is that participants are the only one
who knew that everybody was treated unfairly.
After the dictator allocated 7000 yen, each player
received an allocation sheet that only says how much
she was allocated by the dictator.
Recipient
Recipient
Recipient
500
yen
?
yen
?
yen
Recipient Recipient
?
yen
?
yen
Dictator
? yen
By lottery one player was chosen as a person who
could see the complete distribution of 7000 yen. 29
3) Private knowledge condition
Identical with Common knowledge condition
The recipient who was chosen by lottery knew that
The only difference is that participants are the only one
the
other
recipients
did
not
have
full
information.
who knew that everybody was treated unfairly.
She knew
that she
was the
only
person
who knew
After
the dictator
allocated
7000
yen,
each player
how much
person
received
dictator.
received
an each
allocation
sheet
that onlyfrom
saysthe
how
much
she was allocated by the dictator.
Recipient
Recipient
Recipient
500
yen
500
yen
500
yen
Recipient Recipient
500
yen
500
yen
Dictator
4500 yen
By lottery one player was chosen as a person who
could see the complete distribution of 7000 yen. 30
3) Private knowledge condition
Identical with Common knowledge condition
The recipient who was chosen by lottery knew that
The only difference is that participants are the only one
the
other
recipients
did
not
have
full
information.
who knew that everybody was treated unfairly.
She knew
that she
was the
only
person
who knew
After
the dictator
allocated
7000
yen,
each player
how much
person
received
dictator.
received
an each
allocation
sheet
that onlyfrom
saysthe
how
much
she was allocated by the dictator.
Participant
Recipient
Recipient
Recipient
500
yen
500
yen
500
yen
Recipient Recipient
500
yen
500
yen
Dictator
Since we used deception, actually all
participants were chosen by lottery.
4500 yen
By lottery one player was chosen as a person who
could see the complete distribution of 7000 yen. 31
Hypotheses
There are 3 competing hypotheses regarding cooperation rate.
H1: Only reduction of fear of greed occurs
Participants would cooperate more in both Private and
Common knowledge conditions than in Control condition.
Privately knowing that everybody was treated unfairly
is enough , and common knowledge is unnecessary
60
Hypothetical result
50
Cooperation
rate
40
30
20
10
0
Control condition
Control
Private knowledge
condition
Private
Common knowledge
condition
Common
32
Hypotheses
There are 3 competing hypotheses regarding cooperation rate.
H2: Only reduction of fear of fear occurs
Participants would cooperate more in Common knowledge
condition than in Control and Private knowledge conditions.
Privately knowing that everybody was treated unfairly is
not enough, and common knowledge is necessary
60
Hypothetical result
50
Cooperation
rate
40
30
20
10
0
Control condition
Control
Private knowledge
condition
Private
Common knowledge
condition
Common
33
Hypotheses
There are 3 competing hypotheses regarding cooperation rate.
H3: Both reduction of fear of greed and reduction of
fear of fear occur.
Cooperation rate would be lowest in Control condition and
highest in Common knowledge condition.
Both privately knowing that everybody was treated
unfairly and common knowledge promote cooperation.
60
Hypothetical result
50
Cooperation
rate
40
30
20
10
0
Control condition
Control
Private knowledge
condition
Private
Common knowledge
condition
Common
34
Result (1) Cooperation rate
60
Figure 1:
Cooperation
rate in each
condition
54
50
40
30
30.56
28.21
20
Dummy for Private knowledge condition: β = -0.11, n.s.
10
Dummy for Common knowledge condition: β = 0.98, p<.05
0
%
Control
Control
Private knowledge
Private
Common knowledge
Common
Logistic regression
DV: Cooperation=1, Defection =0
IV: Dummy for Private knowledge cond, Dummy for Common knowledge cond
*Reference category – Control condition
Participants cooperated more in Common knowledge
condition than in the other two conditions.
Hypothesis 2 was supported.
35
Result (2) Effect of expectation
Independent variable
Dummy for Private knowledge
Model 1
Model 2
Model 3
-0.11
0.98*
-0.71
0.34
-1.25+
0.01
Expected cooperation rate
-
26.82 **
-
Estimated probability of the
provision of a public good
-
-
0.07*
Dummy for Common knowledge
The effect of common knowledge disappeared
when we controlled expectation.
Participants cooperated more in Common knowledge
condition because they expected more cooperation by
the others.
This result suggests that reduction of fear
promoted cooperation
36
Summary and Conclusion
Summary
Participants cooperated more in Common
knowledge condition than in the other conditions.
Participants cooperated more only when they knew
that the other participants knew that everybody
was treated unfairly.
Conclusion
Unfair treatment must be a common
knowledge in order to induce a higher level of
cooperation.
This is because such a common knowledge
reduces fear of fear rather than fear of greed.
37
Future directions
Are there any factors other than the sense
of unfairness that promote cooperation by
reducing fear of fear through automatically
activating the perception of common
knowledge?
38
Thank you for your attention.
39
Hypotheses
Cooperation rate
(1) Participants would cooperate more in the unfair treatment
conditions (private and common knowledge conditions) than in the
control condition.
The effect of unfair treatment by the dictator
Private knowledge condition
Common knowledge condition
>
Control condition
(2) Participants would cooperate more in the common
knowledge condition than in the private knowledge condition.
The effect of common knowledge
Common knowledge condition
>
Private knowledge condition
40
Result (1) Cooperation rate
60
Figure 1:
Cooperation
rate in each
condition
54
50
40
30
30.56
28.21
20
Dummy for Private knowledge condition: β = -1.09, p<.05
10
Dummy for Control condition: β = 0.98, p<.05
0
%
Control condition
Private knowledge
condition
Common knowledge
condition
Logistic regression
Dependent variable: Cooperation=0, Defection =1
Independent variable: Dummy for Private knowledge condition
Dummy for Control condition
Common knowledge condition – Reference category
Participants cooperated more in Common knowledge
condition than in the other two conditions.
Hypothesis 2 was supported.
41
Experiment
Control condition : Ordinary one-shot SD without any context
5 players per group
Players first engaged in a social inference task (bogus task), and
were paid 500 yen ($5) for completing the task.
Players were then asked if they want to provide 500 yen to the
group.
If more than 3 players provided 500 yen to the group, everybody
received 800 yen as a bonus. Cooperators receive 800 yen and
defectors receive 1300 yen.
If less then 4 players provided 500 yen, then nobody received a
bonus. Cooperators receive 0 yen and defectors receive 500 yen.
We used deception: Although participants were told that there
were other participants and that they would interact with them,
actually each participant behaves as an individual. In other
words, there was no real interaction with the other participants.
42
Experiment
Control condition : Ordinary one-shot SD without any context
2nd stage: One-shot step level SD
Cooperation : Provide 500 yen to the group
Defection : Keep 500 yen for oneself
500
yen
500
yen
500
yen
500
yen
500
yen
If more than 3 players cooperate, a public good (4000 yen) is
provided.
Total earnings of cooperators : 500-500+(4000/5)=800 yen
defectors : 500-0+(4000/5)=1300 yen
If less then 4 players cooperate, a public good is not provided.
Total earnings of cooperators : 500-500=0 yen
defectors : 500-0=500 yen
43
Experiment
Common knowledge condition
6 players per group
Players first engaged in a social inference task (bogus task), and
were paid 7000 yen as a group.
A dictator was chosen randomly from the group and decided to
allocate 7000 yen among group members.
structure
is identical
with
The dictatorIncentive
allocated 4500
yen for himself
and 500
yen for each
one in the other conditions.
of the other 5the
players.
5 players were then asked if they want to provide 500 yen.
If more than 3 players provided 500 yen to the group, 4000 yen
was forfeited from the dictator and the other 5 players shared 4000
yen equally. In other words, each player received 800 yen.
Successful restoration of fairness
If less then 4 players provided 500 yen, then nothing happens.
Unsuccessful restoration of fairness 44
Experiment
Private knowledge condition
Identical with Common knowledge condition
The only difference is that participants are the only one who knew
that everybody was treated unfairly by the dictator.
After the dictator allocated 7000 yen, each player received an
Incentive
is identical
with by the
allocation
sheet that structure
says how much
she was allocated
dictator. the one in the other conditions.
However, how much the other players’ received was not
written on the allocation sheet.
Then, by lottery one player was chosen as a person who
could see the complete distribution of 7000 yen.
Since we used deception, actually all
participants were chosen by lottery.
45
Result (2) Effect of 2nd-order expectation
What is your estimate of the
other participants’ estimate
of the probability that more
than 3 participants provided
the money?
0.6
0.5
0.4
0.3
0.2
0.1
0
Control
condition
Private
knowledge
condition
Common
knowledge
condition
F（2,124）=6.66, p<.01
2nd-order expectation (expectation on expectation) was
lower in Control condition than in the other 2 conditions.
46
Result (2) Effect of 2nd-order expectation
Independent variable
Model 1
Model 2
Private knowledge
-0.11
-1.00
Common knowledge
0.98*
0.24
2nd-order expectation
-
0.04 **
The effect of common knowledge disappeared when we
controlled 2nd-order expectation.
Participants cooperated more in Common knowledge
condition because they expected the other
participants’ expectation of cooperation higher.
Reduction of fear of fear plays a critical role.
47
Result (2) Effect of expectation
4
0.6
0.5
3
2.71
0.3
2.23
2
0.4
1.86
0.2
0.1
1
0
0
Control
condition
Control condi ti on
Pri v a te k now l edg e
condi ti on
Common k now l edg e
condi ti on
How many participants do you
think have provided the money?
F（2,124）=5.11, p<.01
Private
knowledge
condition
Common
knowledge
condition
What is your estimation of the
probability that more than 3
participants provided the money?
F（2,123）=3.43, p<.05
Participants’ expectation was higher in Common
knowledge condition than in Control condition.
48
Discussion
Participants cooperated more in Common knowledge
condition than in the other conditions.
Participants cooperated more only when they knew
that the other participants knew that everybody
was treated unfairly.
Being treated unfairly makes people
believe that it is a common knowledge.
2nd-order expectation plays a critical role
49