Abstract

Research has established that exposure to a combination of diagnostic (i.e., relevant) and nondiagnostic (i.e., irrelevant) information results in predictions that are more regressive than predictions based on diagnostic information (Hackenbrack, 1992; Hoffman and Patton, 1997). This phenomenon has been labeled the dilution effect (e.g., Tetlock and Boettger, 1989) and has been documented when individuals make predictions. This study tests for the dilution effect when small groups make predictions, and examines the effect of using a procedure designed to reduce the dilution effect. Results indicate that group predictions are influenced by nondiagnostic information in the same manner as are individual predictions, and allowing participants to rate the diagnosticity of information prior to making predictions does not reduce the dilution effect.