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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 legal lore, prior convictions seriously undercut the credibility of the witness and can derail the outcome of a trial. This article suggests that may not always be true. This article 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 wherein believing the plaintiffs story necessarily 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.