Group Size and Cooperation

To compare the effects of group size on cooperation, we introduce a class of simple multiperson games. These games can be regarded as n-person generalizations of the two-person prisoner's dilemma with expected value payoffs. In order to ensure that identical expected-value monetary alternatives are available to players in different-sized groups, we introduced a certain formal constraint on payoffs. Results of an experimental study comparing three-and seven-person groups show that the smaller-sized group is markedly more cooperative than the larger group. The primary emphasis of this paper is methodological. It demonstrates a technique to measure cooperation as a function of group size unconfounded by role-playing and utility considerations.