Are Six Heads as Good as Twelve?
When it comes to group decision-making, does the size of the group matter? We may not doubt that twelve heads are better than one. But are six heads as good as twelve? This is one of the questions asked by research carried out by psychologist and law professor Michael J. Saks, PhD. In a 1977 study, participants were assembled into juries of size six or twelve, shown a videotaped trial, and asked to deliberate to a verdict. Then the researchers measured the process and products of the group decision-making.
Smaller sized groups fostered behavior that would be beneficial for some purposes. But in light of the purposes for which we have juries, most of the advantages favored larger groups. In smaller groups, members shared more equally in the discussion, found the deliberations more satisfying, and were more cohesive. Larger groups were more contentious, debated more vigorously, collectively recalled more evidence from the trial and made more consistent and predictable decisions. The latter finding means that as juries grow smaller, in criminal cases they will make more errors of acquitting the guilty and convicting the innocent. And, in civil cases, not only will the rate of erroneous verdicts rise, but juries will render damage awards that are more unpredictable from case to case (despite similarities in plaintiffs' losses).
In keeping with classic research on the psychology of conformity, because larger groups increase the likelihood that a dissenter will have an ally (or several), those in the minority in larger juries will be better able to resist pressure to yield to group pressure. A later statistical digest of all empirical studies of jury size concluded that larger juries are more likely than smaller juries to contain members of minority groups, more accurately recall trial testimony, spend more time deliberating, hang more often, and reach fewer erroneous decisions. Psychologists who study testing and measurement would not have been surprised by the latter finding, because a basic principle of measurement is that the reliability and validity of almost any measurement is increased (up to a point) when it is judged by a larger number of people.
Saks, M.J. (1977). Jury verdicts: The role of group size and social decision rule. Lexington, MA: D.C. Heath.
Saks, M.J. & Marti, M.W. (1997). A meta-analysis of the effects of jury size. Law & Human Behavior, Vol. 21 pp. 451-467.
The empirical studies are cited in Saks & Marti (above) and many of them are discussed in Justice Blackmun's opinion in Ballew v. Georgia, 435 U.S. 223 (1978).
American Psychological Association, May 28, 2004