What is the impact on juror verdicts of inadmissible evidence that surfaces in the courtroom and of judicial instruction to disregard such information? This question 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 evidence and decreases with pro-acquittal evidence. Second, the research demonstrates that once inadmissible evidence is present, a corrective judicial admonition does not fully eliminate the impact of the inadmissible information.
These conclusions come from a 2006 metaanalysis 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 independent 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 admonished to disregard it, the conviction rate was 10% higher than a no-exposure control group. Of additional 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 motivation also may be affected by reactance—resistance to a judge’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’ ability 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 confusion: 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 admissible. 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 not think of the “white bear” once the thought is forbidden.
Recent experimental research demonstrates that judges, like jurors, have difficulty ignoring inadmissible 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 decisions 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 demonstrates the failure of judicial instruction to effectively eliminate jurors’ use of inadmissible evidence, particularly 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 specific procedural information that they can understand and appreciate. Therefore, remedies may be found in the addition of up-front (pretrial) direction, clear explanations during trial admonitions, and reinforcing charges at the end of the trial. Lessons from broader memory research suggest that any means to intercept errant information before or at the time it is encoded into memory is likely to be more successful than an attempt to remove the inadmissible evidence after it is merged into memory. Jury deliberation also may be expected to limit the influence of inadmissible evidence; however, few studies have addressed this specific hypothesis. The research and legal communities will benefit from future research that attends to creative solutions for the problem of inadmissible evidence.
- Steblay, N., Hosch, H., Culhane, S., & McWethy, A. (2006). The impact on juror verdicts of judicial instruction to disregard inadmissible evidence: A meta-analysis. Law and Human Behavior, 30, 469—192.
- Wistrich, A,. Guthrie, C., & Rachlinski, J. (2005). Can judges ignore inadmissible information? The difficulty of deliberately disregarding. University of Pennsylvania Law Review, 153, 1251-1345.
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