Are Six Heads as Good as Twelve?

Psychologists show how justice is better served by larger juries


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.


Research on jury decision-making by Dr. Saks and others was prompted by two lines of decisions by the U.S. Supreme Court - one involving the jury's size and the other involving its decision rule (how many jurors were required to agree on a verdict in order for that to become the group's verdict?). Here we focus on group size. After 600 years of common law tradition and 200 years of constitutional decisions holding that juries were to consist of twelve people, in the 1970s the Supreme Court reversed itself, reasoning that neither the language of the Constitution nor the intentions of the framers required juries to remain at twelve. The Court said that the correct test was a "functional" one: did smaller juries behave the same as juries of twelve? If their behavior did not differ, then they served the same purposes and were equally constitutional. The Court then answered its own question, mostly by intuition, and concluded that juries of six would perform the job as well as juries of twelve. Thereafter, numerous federal and state courts reduced the size of their juries. But because the Court had framed the constitutional inquiry as an empirical one, the correctness of the Court's guessed answers could be tested by empirical research on jury behavior.

Practical Application

Research by Saks and others suggested that the Supreme Court had erred in its assumptions about the functional equivalence of juries whatever their size. Several government bodies took heed of the research findings. The research was cited as a reason to stop the slide to even smaller juries. When Georgia reduced its criminal juries to five persons, the U.S. Supreme Court called a halt to the shrinkage, held juries smaller than six to be unconstitutional, and in the opinion announcing that judgment the empirical research literature that had developed was extensively cited. Other states entirely refused the invitation to reduce the size of their juries, citing the research on the undesirable consequences of making juries smaller. The Committee on Federal Civil Rules, acknowledging the research findings, took various steps to keep juries larger than the six that the Supreme Court had authorized, at one point trying by rulemaking to restore federal civil juries to the traditional twelve. The U.S. Department of Health and Human Services, seeking to increase the predictability of jury awards in medical malpractice cases, developed a model act for states to follow which called for using juries no smaller than twelve in malpractice cases. As of this writing, the Supreme Court has not yet re-established twelve as the constitutional minimum, but it might yet do so. Psychologists and measurement experts would applaud such a decision.

Cited Research

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.

Additional Sources

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