effort is quantitatively not very different from a group with no Selfish (3.2 vs. 4.1).

As already explained in Section 5.3 the reason for this is that in the “pre-collusion

phase” groups with no Selfish members put in lower efforts than groups with one

Selfish member (average effort is 5.4 in a group of only Other-Regarding vs. 7.5 in a

group with one Selfish prior to the emergence of a Min-Effort Leader). This further

corroborates our result that social preferences seem to matter in complex ways when

communication is possible: Selfish individuals play an important role in facilitating

coordination on the collusive outcome (Hypotheses 2 and 3) while Other-Regarding

have a tendency to put in lower efforts even absent collusive motives (Hypothesis 1).

Thus, we summarize our final primary result, which is consistent with Hypothesis 3:

Result 3: With communication, the propensity to “collude” is greater with one

Selfish group member than with no Selfish group members

For the No Chat treatment, coordinating on a “collusive outcome” was more

diffi cult, since subjects were not able to chat. As shown in Table 6, we find for this

setting that only 1 out of 21 groups end up with minimum efforts in the last 3 periods

and only if the group has no Selfish members. One other group with no Selfish group

members managed to sustain (1, 1, 1) for 3 periods during the course of the game,

but then reverted back to higher effort. If we expand the definition of “collusive”

outcome to include two subjective cases of “collusion” (we report their behavior in

the appendix), then we find one additional group with no Selfish members and one

additional group with 1 Selfish member successfully “collude”by the end of the game.

It seems that collusion is not a main driver of behavior in this treatment and results

seem more consistent with the predictions of the one-shot game.

# Selfish Propensity to “collude” Propensity to “collude”

group members on (1, 1, 1) (self-classification)

0 (14 groups) 7% 14%

1 (5 groups) 0% 20%

2 (2 group) 0% 0%

Table 6: Propensity to “collude” by # of Selfish in the No Chat treatment.

5.4 Robot Treatment

This treatment is similar to the No Chat treatment in the sense that subjects cannot

communicate but are permitted to observe the efforts and payoffs of their group

members after each period. The crucial difference is that in stage 2, instead of

randomly pairing subjects to each other, we paired them to two simulated subjects

we call “robots.” 18 In particular, we programmed 42 robot subjects who react to

18 We provide additional description of this treatment, as well as analysis on the effi cacy of the

robots in our appendix.


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