This article reports the results of a meta-analytic integration of previous research on productivity loss in brainstorming groups. The following patterns were observed: Generally, brainstorming groups are significantly less productive than nominal groups, in terms of both quantity and quality. Stronger productivity Toss was demonstrated in the context of (a) larger groups, (b) experimenter presence, (c) tape-recorded vocalization of contributions (vs. writing of contributions), and (d) in comparison to a nominal group of truly Alone individuals (vs. a nominal group of Together individuals). These patterns are (a) highly consistent with predictions derived from social psychological explanatory mechanisms, and (b) only marginally consistent with procedural explanatory mechanisms, and (c) highly inconsistent with economic explanatory mechanisms. This article considers the implications of these patterns for the use of, and for future research on, brainstorming.