Dilution in legal decision making: Effect of non-diagnostic information in relation to amount of diagnostic evidence

Judgments about others are often based on information that varies in terms of its diagnosticity or usefulness in predicting a certain outcome. Previous studies have demonstrated a “dilution effect” in which the addition of nondiagnostic or irrelevant information yields less extreme judgments than those based solely on diagnostic information. Two studies investigated the dilution effect in a juror decision making context in which no midpoint of a scale was provided by researchers. Study 1 examined the inclusion of positive, negative, or neutral character information in a criminal case and found that this nondiagnostic information affected attitude toward the defendant but did not “dilute” guilt judgments. The cases in Study 1 contained a larger amount of diagnostic information than studies that demonstrated the dilution effect. Thus, the amount of diagnostic evidence provided was varied in Study 2, and the results showed “diluted” judgments only when a small amount of diagnostic information was presented. Limitations to the dilution effect were discussed.