Abstract
Given that group size is known to exert a negative “residual” effect in social dilemmas even when the incentive structure is held constant over different group sizes, it was hypothesized that when no personal contacts were permitted among participants in a one-shot dilemma situation, the residual effect of group size would be mediated either by expectations of other members' contributions or by efficacy of altruistic actions. The results of three experiments in which group size was varied from 2 to 501 (Experiment 1) or 3 to 36 (Experiments 2 and 3) indicate that: (1) the residual effect exists only among small groups; (2) the observed residual effect is mediated by expectations; and, (3) efficacy of altruistic actions does not mediate the observed residual effect.
