APA Dictionary of Psychology

an expectancy-value model of productivity losses in groups that posits that working on a task collectively reduces members’ motivation by lowering their expectations of successful goal attainment and diminishing the value of group goals. See also social loafing; sucker effect. [developed in 1993 by U.S. social psychologist Steven J. Karau (1965–  ) and U.S.-born Australian social psychologist Kipling D. Williams (1953–  )]