EvidenceProf Blog

Editor: Colin Miller
Univ. of South Carolina School of Law

Monday, April 14, 2014

Intriguing Empirical Study of Prior Conviction Impeachment

Kathryn Stanchi (Temple) and Deirdre Bowen (Seattle) recently posted a paper on SSRN summarizing the findings of an experiment they ran on the impact of prior convictions in a mock civil trial. 

This is Your Sword: How Damaging are Prior Convictions to Plaintiffs in Civil Trials? (forthcoming Washington Law Review)

The experiment is cleverly constructed and I recommend the paper to those interested in this topic.  I will add a couple thoughts because while the abstract and some of the language in their paper can be read to suggest that their findings undermine conventional wisdom, I think the study (at least arguably) supports the typical views of many who have studied prior convictions impeachment in the criminal trial context – including myself (see Circumventing Congress: How the Federal Courts Opened the Door to Impeaching Criminal Defendants with Prior Convictions, 42 U.C. Davis L. Rev. 289 (2008))

The authors provided mock jurors with videotapes of a trial and then asked a series of questions.  One group of jurors watched a version where the plaintiff was impeached with a prior conviction for criminal fraud and the other watched the same trial without the impeachment.  (No limiting instruction was supplied).  Surprisingly, jurors who heard about the plaintiff’s prior conviction were more likely to find for the plaintiff!

The authors frame their findings as cutting against the conventional wisdom, but I think their main finding (described above) fits the conventional wisdom quite well.  The conventional wisdom is that prior conviction impeachment is devastating for defendants in criminal cases because it allows jurors to assume that the defendant is “a criminal,” and so more likely -- by propensity -- to be guilty of the charged crime.  The Stanchi-Bowen study reflects no harm to the impeached party, but given the scenario they presented to jurors, this is perfectly consistent with the theory of how prior convictions distort criminal trials.  Stanchi-Bowen showed the mock jurors a civil trial about a traffic accident where the jurors were asked to decide who was the negligent driver.  The fact that the plaintiff had passed bad checks (the prior conviction) is irrelevant either directly or as a matter of propensity reasoning to his care in driving and so the mock jurors did not engage in any propensity reasoning.  Indeed, they may have felt it was a low blow for the defense to bring up the plaintiff’s utterly irrelevant criminal past.

It is clear as well that the study supports the conventional wisdom that the actual legal justification for prior conviction impeachment (that it informs the jury’s assessment of witness credibility) is bankrupt.  The mock jurors did not appear to take the plaintiff’s fraud conviction as a factor that discounted the veracity of the plaintiff’s testimony.  As noted above, jurors who heard about the conviction sided more often with the plaintiff, implicitly crediting his account.

In sum, I think this is an important study and it is more nuanced than can be reflected in this blog post, so it is highly recommended reading.  To my mind, however, the study does more to support the conventional academic critique of prior conviction impeachment than undermine it.

Here is the abstract:

"The conventional wisdom in law is that a prior conviction is one of the most powerful and damaging pieces of evidence that can be offered against a witness or party. In the legal lore, prior convictions seriously undercut the credibility of the witness and can derail the outcome of a trial. This paper suggests that may not always be true.

This paper details the results of an empirical study of juror decision-making that challenges the conventional wisdom about prior convictions. In our study, the prior conviction evidence did not have a direct impact on the outcome of the civil trial or the credibility of the witness with the conviction. Moreover, we tested prior conviction evidence with a white witness and an African-American witness and saw no difference in results.

The prior conviction evidence did, however, change the trial in a substantial, but indirect, way. Rather than the direct effect on outcome that we might have expected, the introduction of the prior conviction evidence changed the mental decision-making process of the jurors. Specifically, the evidence seemed to subconsciously lead the jurors to conclude that to decide liability, they had to believe one party over the other. The prior conviction evidence thus turned the trial into a zero sum credibility contest in which believing the plaintiff’s story meant disbelieving the defendant’s (and vice versa). This “zero sum” effect did not appear in the control version of the trial.

In sum, the results of our experiment suggest that while prior convictions are highly noticeable and powerful pieces of evidence, they may not always be the bane that lawyers think they are. Nevertheless, the introduction of this evidence has the potential to change a civil trial by changing the juror decision-making process."


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