Table 1.

Punishment and cooperation levels. Ordinary least squares regressions with the group average contributions of all groups, which show any variation in contributions as independent observation (n = 273). The group average contributions over periods 2 to 10 are the dependent variables. The independent variables are the group average contributions in period 1, the group averages of punishment points assigned to group members who contributed less than the punishing participant (group average punishment of free riding) and to group members who are equally or more cooperative than the punishing participant (group average antisocial punishment). Model 1 does not control for the mean cooperation level in a participant pool, whereas model 2 controls for it by adding participant pool dummies. The adjusted r2 increases by only 7% and the results remain robust, although the coefficient for antisocial punishment is reduced in size. *P < 0.1, **P < 0.05, ***P < 0.01. Numbers in parentheses indicate robust standard errors.

Dependent variable: group average contributions in period 2 to 10
1 2
Group average contributions in period 1 0.779*** (0.052) 0.720*** (0.065)
Group average punishment of free riding 0.521** (0.201) 0.480** (0.200)
Group average antisocial punishment -2.247*** (0.350) -1.256*** (0.325)
Constant 5.057*** (0.688) 5.899*** (1.221)
Participant pool dummies No Yes
Adjusted r2 0.60 0.67
F test 136.9 31.3
P value 0.000 0.000
N 273 273