"The jury will disregard the defendant's ski mask and machete": how effective are instructions to disregard evidence?

Effective?

Judges often instruct jurors to “disregard” certain inadmissible information presented at trial. How effective is such an instruction? How realistic is it for jurors to disregard information after they have heard it, especially if the information is incendiary? Even if the information is not discussed during deliberations, is it possible for the information not to affect the outcome?

A 1988 experiment conducted at Northwestern University measuring the effect of such instructions on jury awards yielded very interesting results. The mock jurors were divided into thirds and were asked to awarded damages in a mock trial where a police officer was sued for illegally searching the plaintiff. 

• The first third of jurors learned that the allegedly illegal search turned up wrongdoing by the plaintiff and were instructed to disregard it by the judge. 
• The second third heard that no evidence of wrongdoing was apparent. 
• The final third did not receive information on the outcome of the search. 
• Perhaps unsurprisingly, “[j]urors who learned that the search had turned up wrongdoing were unable to disregard that information, even when ordered to do so.” In fact, in mock cases where jurors learned that a plaintiff was in possession of heroin, punitive damages were awarded only 38% of the time, which is 23-24% less than the other two thirds who learned the victim was innocent or knew nothing at all. 
• Why?: Professor Casper (who led the research) determined from post-mock trial interviews that the jurors’ decisions were “probably the result of an unconscious interpretation and recall testimony of the trial" because knowing the plaintiff was guilty of wrongdoing "affected the jurors' recollection of lawyers' arguments" and other information.

 Another very meticulous study from 2006 measured the impact of inadmissible evidence on jury decisions. “First, the aggregate data indicate that the presence of inadmissible evidence affects verdicts in line with the evidentiary slant of the information. The level of guilty verdicts increases with pro-prosecution evidence and decreases with pro-acquittal evidence.” Furthermore, the study showed that once inadmissible evidence has made a significant impact on as jury, “a corrective judicial admonition does not fully eliminate the impact.”

Significantly, the study discussed the rationale behind juror failure to follow instructions to disregard inadmissible evidence. When the reason for rejection of inadmissible evidence is inadequate, a jury is more likely to allow the evidence to impact the outcome. However, when the judge explains his reasoning behind the rejection, the inadmissible evidence has a smaller impact on the outcome.[1] This suggests that a solution to the negative effects of inadmissible evidence is simply to provide adequate justification to the jury for striking evidence. For example, a judge should explain that the evidence is irrelevant to the case or is unfair or manipulative.

However, this may not be sufficient. A 1997 studying measuring jurors’ response to different categories of inadmissible evidence found that “jurors comply with an instruction to disregard when evidence is inadmissible due to a lack of credibility but not when it is excluded due to a legal technicality.”  Thus, the “attribution” for the judge’s ruling has a psychological impact on the jury, whether or not the jurors may be aware of that fact.[2]

What is the solution in that type of situation, then, when a piece of evidence must be disregarded for procedural reasons? Well, if you’ve read my previous blog post on the rapidly shrinking attention span of jurors, hopefully nobody was paying attention in the first place.

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[1] Nancy, Steblay, Harmon M. Hosch, Scott E. Culhane, & Adam McWethy, The Impact on Juror Verdicts of Judicial Instruction to Disregard Inadmissible Evidence: A Meta-Analysis, 30,

 Law and Human Behavior, 469, 487 (2006).

[2] Saul M. Kassin & Samuel R. Sommers, Inadmissible Testimony, Instructions to Disregard, and the Jury: Substantive Versus Procedural Considerations, 23 PSPB 1046, 1051 (1997).