INADMISSIBLEEVIDENCE,
IMPACT ONJURIES
What is the impact on juror verdicts of inadmissible
evidence that surfaces in the courtroom and of judicial
instruction to disregard such information? This ques-
tion has been addressed in laboratory research by
attention to its two component parts. First, the
research establishes that the presence of inadmissible
evidence has a significant impact on juror verdicts in
line with the evidentiary slant of the information: The
level of guilty verdicts rises with pro-prosecution evi-
dence and decreases with pro-acquittal evidence.
Second, the research demonstrates that once inadmis-
sible evidence is present, a corrective judicial admoni-
tion does not fully eliminate the impact of the
inadmissible information.
These conclusions come from a 2006 meta-
analysis that summarized 175 experimental tests,
from 48 studies and 8,474 research participants.
Confidence in the findings is strengthened by the
demonstrated convergence of data from multiple inde-
pendent labs; 42 research teams contributed to the
data set, no more than 6 tests coming from any one
lab. Ninety-one percent of the tests involved criminal
cases. Civil and criminal cases showed similar effects.
The greatest number of laboratory tests involve
inadmissible evidence that favors the prosecution in
criminal cases. When research participants heard
problematic pro-prosecution evidence and were admon-
ished to disregard it, the conviction rate was 10%
higher than a no-exposure control group. Of addi-
tional interest is the finding that exposure to contested
evidence that was subsequently ruled admissible
accentuated that information, raising conviction
rates 34% above the control group and significantly
strengthening the impact of that evidence beyond its
original influence.
Inadmissible evidence violates due process, and
legal evidentiary standards dictate that a curative
instruction is appropriate to minimize the risk that
the jury is misled by the unacceptable information.
Psychologists posit that jurors are likely to follow the
prescribed corrective action only if motivated and able
to do so. Research shows that jurors do attempt to use
information in a fair manner and to align their decisions
with the judge’s instructions. However, juror motiva-
tion also may be affected by reactance—resistance to ajudge’s admonition when it is seen as constraining
effective deliberation—unless the judge can offer a
clear and compelling reason as to why the information
is unreliable or irrelevant to the case. Jurors may resist
giving up information that they find probative.
Even when they are motivated to do so, jurors’ abil-
ity to effectively purge inadmissible evidence from
their decision making is questionable. At times, the
problem may be one of disentangling an inadmissible
element from a broader coherent “story” that has
developed in the juror’s mind and of separating out
any inferences that grow from that bit of evidence.
Contamination of a juror’s knowledge by inadmissible
evidence may be exacerbated by simple source confu-
sion: As the trial proceeds, jurors may misremember
the origin of a piece of information—for example,
nonevidentiary pretrial publicity versus testimony
evidence—or fail to recall whether it is legally admis-
sible. In addition, contested evidence is likely to
become salient to jurors, and the judge’s subsequent
instruction to disregard the information may produce
what researchers refer to as a “white bear effect”—an
inability to notthink of the “white bear” once the
thought is forbidden.
Recent experimental research demonstrates that
judges, like jurors, have difficulty ignoring inadmissi-
ble evidence. Specifically, the decisions of a sample of
265 judges in simulated cases were shown to be
affected by nonevidentiary information from pretrial
settlement proposals, conversations protected by
attorney-client privilege, prior sexual history of a rape
victim, prior convictions of a plaintiff, and defendant
cooperation with the government. An impact on deci-
sions was apparent even when the judges were
reminded or they determined that the information was
inadmissible. This sample of judges, however, was
able to disregard information obtained in violation of
a defendant’s right to counsel and as the outcome of a
search when deciding on probable cause issues.
Directed forgetting of inadmissible evidence prompts
a very difficult cognitive task. Research firmly demon-
strates the failure of judicial instruction to effectively
eliminate jurors’ use of inadmissible evidence, particu-
larly in the absence of a good reason for rejecting the
information. Far less research has addressed potential
solutions to this problem. Jurors do respond to spe-
cific procedural information that they can understand
and appreciate. Therefore, remedies may be found
in the addition of up-front (pretrial) direction, clearInadmissible Evidence, Impact on Juries——— 369I-Cutler (Encyc)-45463.qxd 11/18/2007 12:43 PM Page 369