In the United States, criminal defendants who face serious felony charges are almost always afforded the right to a trial by a 12-member jury. A few states, however, allow these trials to proceed before six-member juries, even when a defendant faces a mandatory life sentence. Although researchers have had much to say about the relative performance of six- and 12-member juries, the legal impact of this research has been mixed.
In Williams v. Florida (1970), the Supreme Court held that Florida's use of six-member juries in criminal cases does not violate a defendant's Sixth Amendment right to a jury trial. In reaching this conclusion, the court found that despite centuries of tradition, the term "jury," as it is used in the Sixth Amendment, does not necessarily refer to a group of exactly 12. The Constitution requires only that a body possesses "the essential feature of a jury," the court explained. Specifically, the body must provide a safeguard against corrupt or overzealous prosecution by interposing "commonsense judgment" between the accuser and accused, and its verdicts must reflect "community participation and shared responsibility."
In finding that six-member juries possess these essential features, the court noted that there is no meaningful difference between six- and 12-member juries' effectiveness in 1) promoting group deliberation; 2) insulating members from outside intimidation; and 3) providing a fair chance "for obtaining a representative cross-section of the community." The court also noted that the "few experiments" that had been conducted "indicate that there is no discernable difference between the results reached by the two different-sized juries."
After Williams, researchers conducted several new studies to investigate whether six- and 12-member juries differ in meaningful ways. In a 1997 meta-analysis, Michael Saks, PhD, MSL, and Mollie Marti, PhD, JD, identified three key findings that emerged from these studies. First, research indicates that 12-member juries are more likely than six-member juries to include members of a racial minority. This finding, which is reinforced by the recent work of Shari Diamond, JD, PhD, et al. (in press), speaks directly to Williams's assumption that smaller and larger juries do not differ in their ability to fairly represent the community. Second, the meta-analysis found that there is evidence that 12-member juries accurately recall more evidence and deliberate slightly longer than six-member juries. It should be noted, however, that research has not shown that juries of different sizes reach different verdicts—which is consistent with the Williams court's interpretation of the available literature. Finally, research suggests that 12-member juries are more likely to deadlock, or "hang," than six-member juries.
In Ballew v. Georgia (1978), the Supreme Court held that reducing the number of jurors below six created a "substantial threat" to constitutional rights that could not be justified by the state's interest in saving time and costs. Many of the research findings summarized above influenced the court's decision, even though the underlying studies focused on differences between six- and 12-member juries. Nevertheless, the court has so far been unwilling to re-examine the question whether, in light of current research, six-member and 12-member juries are functionally equivalent. Indeed, last winter the court declined to hear Deltoro v. Florida and Gonzalez v. Florida, which called for reconsideration of Williams's "jury size" holding.
Though much work has been done, further research is needed on the differences between six- and 12-member juries. For instance, although research has consistently shown that six-member juries are not likely to represent the community as effectively as 12-member juries, studies on the other components of the Williams decision have yielded more equivocal findings: Observed differences in deliberation quality and quantity have not been associated with differences in verdict decisions, and little if any research has focused on smaller juries' ability to resist external influences. Also, future research might help identify the "optimum" number of jurors for balancing the principles articulated in Williams with other values, such as cost savings and avoiding deadlocks. Alternately, given the Supreme Court's reluctance to revisit Williams, psychologists might seek to identify strategies for improving the quality of six-member juries' deliberations. For example, recent research suggests that note-taking may limit some of the differences in civil damages awarded by larger and smaller juries (e.g., Irwin Horowitz, PhD, & Kenneth Bordens, PhD, 2002).