Group size and the performance of a composite group majority: Statistical truths and empirical results

The judgmental accuracy of group majority decision making in binary choice, multiple-item prediction tasks as a function of group size, average competence of group members, and the shape of the overall distribution of judgmental accuracy in the group are discussed. For the case where the addition of an (N + 1)th member to a group of size N has a known cost function and the value of a correct group decision can be specified, the optimal group size is calculated.