The effects of outlier presence, plaintiff population size, and aggregation of plaintiffs on simulated civil jury decisions.

Horowitz, I. A., & Bordens, K. S. (1988). The effects of outlier presence, plaintiff population size, and aggregation of plaintiffs on simulated civil jury decisions. Law and Human Behavior, 12, 209-229.

An experiment was performed to determine the effects of the size of the plaintiff population, the presence or absence of an outlier, defined as a plaintiff whose injuries were significantly more severe than other plaintiffs, and whether plaintiffs were tried individually or were aggregated in a group. Sixty-six person juries were assigned to one of eleven experimental conditions, listened to a 4-h toxic tort trial, and, after deliberating, delivered verdicts on liability, and damage awards. The verdicts were increased significantly by the presence of an outlier and by an increase in the plaintiff population. While the punitive awards were higher in the outlier condition, there was also a tendency for juries to find the company not liable. The meaning of the above findings, as well as the fact that juries exhibited great variability in their verdicts was discussed. Evidence as to the decision-making process of the juries was also gathered and discussed.

Presence of “outlier” plaintiff with very serious injury, and size of injured plaintiff population, associated with larger punitive damages; outlier plaintiff increased variability of punitive damages. No impact of either on compensatory damages. Plaintiff with least injury benefited from unitary trial structure.

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