Productivity loss in brainstorming groups: Toward the solution of a riddle.

We conducted four experiments to investigate free riding, evaluation apprehension, and production blocking as explanations of the difference in brainstorming productivity typically observed between real and nominal groups. In Experiment 1, we manipulated assessment expectations in group and individual brainstorming. Although productivity was higher when subjects worked under personal rather than collective assessment instructions, type of session still had a major impact on brainstorming productivity under conditions that eliminated the temptation to free ride. Experiment 2 demonstrated that inducing evaluation apprehension reduced productivity in individual brainstorming. However, the failure to find an interaction between evaluation apprehension and type of session in Experiment 3 raises doubts about evaluation apprehension as a major explanation of the productivity loss in brainstorming groups. Finally, by manipulating blocking directly, we determined in Experiment 4 that production blocking accounted for most of the productivity loss of real brainstorming groups. The processes underlying production blocking are discussed, and a motivational interpretation of blocking is offered. In his influential book, Osborn (1957) suggested brainstorming as a method of group problem solving that considerably increases the quality and quantity of ideas produced by group members. Brainstorming groups are traditionally given instructions designed to free the individual members from the inhibiting effects of self-criticism and the criticism by others during the problem-solving session. The rules behind brainstorming are as follows: keep in mind that the more ideas the better and the wilder the ideas the better, improve or combine ideas already suggested; and do not be critical. Osborn (1957) claimed that if these rules are followed "the average person can think up twice as many ideas when working with a group than when working alone" (p. 229).