a subject of research by psychologists and other social
and behavioral scientists. The number of jurors and
the minimum proportion of them who must be in
agreement are set by formal legal rules (e.g., state
statutes, federal rules of civil procedure), and those
rules are in turn subject to constitutional require-
ments. The Supreme Court has framed its analysis of
jury size and decision rule questions in terms of the
effects of those variables on jury behavior. Thus, the
findings of research on group decision making as a
function of group size and social decision rule are of
central relevance to the Court’s constitutional analy-
sis. Yet a considerable tension exists between the
Court’s conclusions and the empirical findings.Jury Size
For 600 years of common-law history and 200 years
of American constitutional history, the jury was con-
sidered to have 12 members. But several states and
federal districts in the United States began to use
smaller juries, and in the 1970s, challenges to the use
of juries with fewer than 12 members reached the
U.S. Supreme Court. The Court analyzed the consti-
tutionality of smaller juries by rejecting the guidance
of history, tradition, and its own precedents. Instead,
the Court reasoned that because the size of the jury
was not specified in the Constitution and the framers’
intentions regarding jury size could not be divined,
the answer would have to be found through a “func-
tional” analysis of the jury’s purpose: If smaller juries
did not behave differently from juries of 12, then they
were their functional equivalent and therefore were
constitutional.
In a series of cases—Williams v. Florida(1970)
(state criminal juries of 6),Colgrove v. Battin(1973)
(federal civil juries of less than 12), and Ballew v.
Georgia(1978) (state criminal juries numbering 5)—
the Supreme Court held smaller juries to be constitu-
tionally permissible because it found no important
differences between 6- and 12-member juries in the
reliability of their fact finding, the quality or quantity
of their deliberation, their cross-sectional representa-
tion of the community, the ability of jurors in the
minority to resist the social pressure to conform, or
their verdicts. These findings were reached through a
combination of judicial intuition, misconstruing non-
studies as empirical studies, misreading the findings
of actual empirical studies, and failing to see elemen-
tary flaws in actual empirical studies.What the empirical research findings actually indi-
cate is that smaller groups foster behavior that is ben-
eficial in some respects, but in view of the purposes
for which juries are employed, most of the advantages
appear to favor keeping juries at 12. On the positive
side, in smaller juries, members share more equally in
the discussion, find the deliberations more satisfying,
and are more cohesive.
A meta-analysis of studies specifically of juries
(both simulated and actual) found that larger juries are
more likely than smaller juries to contain members of
minority groups, deliberate longer, hang more often,
and recall trial testimony more accurately. Turning to
studies of small-group behavior generally, one finds
that larger groups tend to discuss and debate more vig-
orously, collectively recall more information, and make
more consistent and predictable decisions. The latter
finding means that as juries grow smaller, they will tend
in criminal cases to make more errors of acquitting the
guilty or convicting the innocent; and in civil cases, not
only will the rate of erroneous verdicts rise, but juries
will tend to render damage awards that are more vari-
able and unpredictable. (Because such differences will
be small, very large sample sizes would be necessary to
detect them.) In accord with classic research on the psy-
chology of conformity, because in larger groups there is
greater likelihood that a dissenter will have at least one
ally, a dissenter in larger juries will usually find an ally
and therefore be better able to resist the pressure to sub-
mit to the majority.
In short, the Williams Court had scant support for
its conclusion that “there is no discernible difference
between the results reached by the two different-sized
juries”; the little research evidence that existed then
and most of the evidence that developed later sup-
ported the opposite conclusion: that 6-person juries
did behave differently from 12-person juries and most
of those differences represented less-desirable deci-
sion-making processes.
In the Ballewcase, the Supreme Court drew the
line, holding juries of 6 to be the constitutional
minimum. Justice Harry Blackmun’s opinion announc-
ing the judgment of the Court extensively reviewed
the empirical research on the subject, much of it
having been prompted by the Williams decision.
Curiously, although the research summarized in the
opinion mostly compared 6- and 12-person juries and
indicated that the former did not perform as well as
the latter, the Court did not reverse its earlier holdings.
Instead, it reaffirmed the earlier decisions finding424 ———Jury Size and Decision RuleJ-Cutler (Encyc)-45463.qxd 11/18/2007 12:43 PM Page 424