Despite the popular belief that group of individuals brainstorming together can generate more and better ideas than individuals brainstorming alone, many empirical studies have found that the productivity of interacting groups is inferior to the combined output of an equal number of people brainstorming alone, in terms of both the quantity and quality of ideas. We hypothesized that members of interacting groups may focus on the total group product and derive an inflated sense of accomplishment compared with individual brainstormers who only perceive their individual product. We expected that providing a standard of productivity for interacting (brainstorming) groups would reduce productivity loss. We conducted an experiment using a 3×2 factorial design with group size (singleperson, 2-person, and 4-person group) and standard condition (standard vs. no standard) as independent variables. The topic for brainstorming was the practical benefits and difficulties that would arise if everyone after 1991 had an extra thumb on each hand. Our results suggest that even though individuals in interactive groups produce relatively fewer ideas, they perceive their performance more positively than individuals in nominal groups. However, while misperception of task performance does occur in group settings, it does not account completely for productivity loss in brainstorming groups.