Asymmetric influence in mock jury deliberation: jurors' bias for leniency.

Investigators have frequently noted a leniency bias in mock jury research, in which deliberation appears to induce greater leniency in criminal mock jurors. One manifestation of this bias, the asymmetry effect, suggests that proacquittal factions are more influential than proconviction factions of comparable size. A meta-analysis indicated that these asymmetry effects are reliable across a variety of experimental contexts. Experiment 1 examined the possibility that the leniency bias is restricted to the typical college-student subject population. The decisions of college-student and community mock jurors in groups beginning deliberation with equal faction sizes (viz., 2:2) were compared. The magnitude of the asymmetry effect did not differ between the two populations. We hypothesized that the asymmetry effect was caused by an asymmetric prodefendant standard of proof--the reasonable-doubt standard. In Experiment 2, subjects received either reasonable-doubt or preponderance-of-evidence instructions. After providing initial verdict preferences, some subjects deliberated in groups composed with an initial 2:2 split, whereas other subjects privately generated arguments for each verdict option. A significant asymmetry was found for groups in the reasonable-doubt condition, but group verdicts were symmetrical under the preponderance-of-evidence instructions. Shifts toward leniency in individual verdict preferences occurred for group members, but not for subjects who performed the argument-generation task. The theoretical and applied significance of these findings is discussed.