This study investigated in which group tasks (disjunctive/additive) the “80/20 rule” was observed. The “80/20 rule” refers to an empirical rule where a group or organization is composed of some active members and many inactive members. The situation that follows the process of the “80/20 rule” is little known in human social behavior. Thus, we examined whether the behavioral equilibrium according to the “80/20 rule,” where the workload of a few active members increases and that of other inactive members decreases, could be observed using two types of group tasks. Seventy-five undergraduates participated in an experiment. They completed five trials of a mathematical task in groups of four or five. The participants were told that the experimental reward would be determined either by the score of the group member who solved the most answers (disjunctive task) or by the average of the scores of all members (additive task). The results showed no behavioral equilibrium following the “80/20 rule” in both tasks. The limitations of this study were discussed.
