during memory storage (retention interval), and at
memory test. The more nearly ideal the processing con-
ditions are for witnesses, the more they should be able
to track accurately the adequacy of their memory per-
formance in overtly expressed confidence ratings. The
context in which the optimality hypothesis was pro-
posed is discussed next.
By the end of the first decade of the modern resur-
gence of interest in conducting research concerned with
the psychology of testimony, several dozen studies had
accumulated wherein both witness accuracy and confi-
dence in their identification decisions was measured.
The commonsense intuition of laypersons, jurists, and
researchers alike was that witness confidence should
accurately track witness accuracy. In addition, signal
detection theory, perhaps the most widely accepted the-
ory of human judgment, made the same prediction.
That is, the expectation was that when the accuracy of
an identification decision made by each of a number of
witnesses was correlated with a measure of their confi-
dence in their decisions, the correlation coefficient
expressing the predictability of accuracy from
expressed confidence should be positive and relatively
strong. The problem was that the empirical findings in
this regard were decidedly mixed. Approximately half
these initial studies reported positive correlation coeffi-
cients, ranging from +.20 to +.95, and the other half
reported either correlation coefficients not statistically
different from 0 or reversed (negative) correlations of
witness accuracy and certainty.
At least on the surface, there would appear to be
equal arguments both for and against the prior expec-
tation that witness confidence should track witness
accuracy with reasonable fidelity. In an effort to
resolve this apparent contradiction of expectation and
to account for the very large range of obtained corre-
lation coefficients, a close examination of the studies
in question revealed that there was substantial statisti-
cal support for the optimality hypothesis. Studies
were first classified as having provided either high
optimal or low optimal information processing condi-
tions for witnesses. High optimal studies were defined
as those wherein overall accuracy was at least 70%
and that possessed at least three of the following infor-
mation-processing conditions: warning of an impend-
ing memory test, stress levels low enough to permit
adequate monitoring of the environment, ample
opportunity to observe the target person, a brief reten-
tion interval, high familiarity with the target, similar
condition of the target at encoding and memory test,low similarity of the target to foils (an innocent person
in a police lineup) at test, unbiased memory test
instructions, and additional consistent information
presented during the retention interval. Then, both the
number of significant positive accuracy-confidence
correlation coefficients and the number of not signifi-
cant or reversed accuracy-confidence correlations
were determined for each category of study, those
possessing of high and those possessing low optimal
processing conditions. Fully 77% of studies had either
high optimal processing conditions and a significant
positive accuracy-confidence correlation or low opti-
mal conditions and a not significant or reversed corre-
lation coefficient. This proportion of cases is
significantly greater than the proportion (.23) of cases
wherein high optimal conditions resulted in not sig-
nificant or reversed correlation coefficients or low
optimal conditions produced significant positive cor-
relations. Further analysis showed that this strong sup-
port for the optimality hypothesis was not related to
whether the information-processing conditions in a
study were of greater or lesser forensic relevance.
Since the proposal of the optimality hypothesis,
publication of substantially greater numbers of inves-
tigations in which accuracy-confidence correlations
were computed has occurred, and at least two meta-
analyses (assessments of the average effect size, for
the accuracy-confidence correlation in this case) have
been conducted. As a result, two conclusions may be
drawn. First, the average effect size has been esti-
mated to be in the range of +.25 to +.35. That is, only
6% to 12% of the variation in accuracy judgments can
be explained by variations in witness confidence. This
result can be contrasted with the finding in one study
that variations in juror perceptions of witness confi-
dence accounted for as much as 50% of the variance
in juror judgments as to witness accuracy. Second,
additional empirical support for the optimality
hypothesis has been obtained. In one published meta-
analysis, clear evidence was found of longer target
exposures being associated with a higher accuracy-
confidence correlation (+.31) than shorter target face
exposures (+.19). Other separate empirical investiga-
tions have found moderately strong positive correla-
tions between target face distinctiveness and the size
of the accuracy-confidence correlation. Still other
studies have obtained markedly higher accuracy-
confidence correlations in no-disguise conditions ver-
sus disguise conditions and in conditions with lower
stress than in conditions with higher witness stress.Optimality Hypothesis in Eyewitness Identification——— 531O-Cutler (Encyc)-45463.qxd 11/18/2007 12:43 PM Page 531