The effect of jury deliberations on jurors’ reasoning skills.

McCoy, M. L., Nunez, N., & Dammeyer, M. M. (1999). The effect of jury deliberations on jurors’ reasoning skills. Law and Human Behavior, 23, 557-575.

The effect of jury deliberation on jurors’ reasoning skill in a murder trial was examined. Specifically, the effect of deliberating on reasoning competence (as defined by Kuhn, Weinstock and Flaton, 1994) was explored. One hundred and four participants viewed a videotaped murder trial and either deliberated in 12-person juries or ruminated on the case individually. Among those assigned to juries, half had their reasoning skill assessed prior to deliberations, while the others were tested after deliberating. Jurors in the individual rumination condition were assessed after they had the opportunity to reflect on the case alone. As hypothesized, post-group-deliberation jurors were more likely to discount both the selected verdict and alternative theories and incorporate judgmental supporting statements than were the other mock jurors. However, the mock jurors did not differ with regard to making statements that supported alternative verdicts or including judgmental statements that discounted their chosen verdict. In terms of Kuhn’s reasoning continuum from satisficing (low level) to theory-evidence coordination (high level), there is some evidence that post-group-deliberation jurors may be closer to the high end than predeliberation jurors or post-individual-rumination jurors in some aspects of the task, but not in others.

Deliberating jurors showed somewhat higher levels of reasoning than individuals who did not deliberate, where reasoning was defined in terms of systematically matching the evidence to alternative verdict options.