Table 4. Comparison between predictions of the cooperative equilibrium and experimental data in the PGG. In Condition S, the cooperative equilibrium coincides with the Nash equilibrium. In Condition L, it predicts that players should contribute about 35% of their endowment. CE correctly predicts a positive effect of group size on cooperation.

Condition	Mean contribution	CE prediction
S	3.92	0
L	6.91	3.46