Group choice: The ideal free distribution of human social behavior

Group choice refers to the distribution of group members between two choice alternatives over time. The ideal free distribution (IFD), an optimal fora ging model from behavioral ecology, predicts that the ratio of foragers at two resource sites should equal the ratio of obtained resources, a predicti on that is formally analogous to the matching law of individual choice, exc ept that group choice is a social phenomenon. Two experiments investigated the usefulness of IFD analyses of human group choice and individual-based e xplanations that might account for the group-level events. Instead of nonhu man animals foraging at two sites for resources, a group of humans chose bl ue and red cards to receive points that could earn cash prizes. The groups chose blue and red cards in ratios in positive relation to (lie ratios of p oints associated with the cards. When group choice ratios and point ratios were plotted on logarithmic coordinates and fitted with regression lines, t he slopes (i.e., sensitivity measures) approached 1.0 but tended to fall sh ort of it (i.e., undermatching), with little bias and little unaccounted fo r variance. These experiments demonstrate that an IFD analysis of group cho ice is possible and useful, and suggest that group choice may be explained by the individual members' tendency to optimize reinforcement.