Jury: Behavioral Aspects

One way to evaluate jury behavior is to compare the decisions reached by juries with those reached by judges. Studies of judge-jury agreement reveal substantial, but not uniform agreement. In Kalven and Zeisel's classic study of jury trials, judges reported the jury verdicts for each of the jury trials over which they presided. They also indicated how they would have decided the cases if they had been bench trials. In 78 percent of the cases, the judge and jury agreed on the verdict. In disagreement cases, the judge would have convicted when the jury acquitted in 19 percent of the cases and the jury convicted when the judge would have acquitted in 3 percent of the cases, a net leniency of 16 percent.

When disagreement arose, it was not attributable to case complexity. Cases that the judge rated as high in complexity were no more likely to stimulate disagreement between the judge and jury than were cases that were low in complexity. The disagreements emerged most often (in 45 percent of the disagreement cases) from the combination of a difference in interpretation of the evidence (the jury's traditional fact-finding role) and an issue of values (e.g., the jury's preference for an expanded version of the law of self-defense). Different conclusions about the facts alone accounted for 34 percent of the disagreements, and values alone accounted for only 21 percent of the disagreements.

Kalven and Zeisel collected their data in the late 1950s, but despite many changes in the makeup of the jury pool and the bench, a very similar pattern was found more recently by Heuer and Penrod. In a sample of criminal trials, they obtained a rate of 74 percent agreement, with the judge convicting when the jury would have acquitted in 23 percent of the cases and the jury convicting when the judge would have acquitted in 3 percent of the cases, a net leniency of 20 percent.

A few researchers have examined the impact extra-legal factors, such as inadmissible evidence, or judicial decisions. The results suggest that judges as well as jurors are susceptible to cognitive biases that can influence their verdicts.