Guilt beyond a reasonable doubt: Effects of concept definition and assigned decision rule on the judgments of mock jurors.

Examined the concept of reasonable doubt as both an individual and group decision criterion. Previous research indicates that neither criterion has an effect on verdicts. A reexamination of this research suggested that such effects might occur for cases producing maximum disagreement. An experiment was performed in which 606 mock jurors reached individual and group verdicts for such a case. The decision criteria for individuals (judge's definition of reasonable doubt) and groups (assigned decision rule) were varied in a factorial design. As predicted, mock juries assigned a unanimity decision rule were significantly less likely to reach a verdict than juries assigned a majority rule. Minority members of juries assigned a majority decision rule were particularly dissatisfied with group deliberation. Definitional variations in reasonable doubt significantly affected both individual and group verdicts. The effects of the independent variables for the group decision-making process were also examined using a model-fitting approach to J. H. Davis's.