The Advantage Blog

Jurors bias evidence to help “their side”

August 11, 2014 | By |

When I studied juror decision-making in graduate school, I was most concerned about the ecological and external validity of my research. That is, does the design of the study sufficiently replicate real life and are the findings generalizable to the real world? Given that I was studying juror decision-making in a lab, employing undergrads as “jurors”, and using a condensed trial transcript as my stimuli, it’s easy to see that these were legitimate concerns. However, after recently wrapping up yet another shadow jury project, I am more and more confident that research findings do reflect actual juror decision-making.

In my research, I examined a phenomenon in decision-making called predecisional distortion. Basically, this is the tendency for people to bias new evidence in favor of their current leaning. Jurors often give new evidence more or less weight depending on whether or not it conforms to that particular juror’s leaning. In other words, a juror who is leaning toward the plaintiff will give more weight to the impact of evidence that favors the plaintiff and discount the impact of strong evidence for the defense. This is not to say they outright ignore the disconfirming evidence (although they may), but it’s more likely that the evidence will simply have less impact on the plaintiff-leaning juror than it will on a neutral juror or a defense-leaning juror. As with most cognitive biases, this process generally occurs automatically and at an unconscious level.

When we interview shadow jurors each day following trial, we assess their current leaning, in addition to the impact of evidence, areas of confusion, witness credibility, and so on. Over the many days of trial, it is easy to see this predecisional distortion take hold: the plaintiff-leaning shadow jurors find defense evidence less impactful than the defense-leaning shadow jurors, and vice versa. As a result, they usually only show minor shifts in their general leaning throughout trial (rather than wild fluctuations from one side to the other). Over the course of the trial, the strength of the shadow juror’s leaning typically becomes stronger and more extreme, an effect I call “leaning polarization.”

One way attorneys can combat predecisional distortion, or, more accurately, take advantage of predecisional distortion, is to focus on creating a compelling opening statement to push jurors to their side immediately. This may then have an impact on how jurors interpret and weigh evidence throughout the trial. Jury selection is also critical, as any bias jurors have before a trial begins may determine how they evaluate the evidence. In fact, my research assessed leanings before the “jurors” had heard anything other than a neutral statement, and these leanings predicted predecisional distortion and verdicts. Taken together, the research (both in the lab and in the field) demonstrates that the first few days of trial are critical in determining how evidence will be accepted as trial progresses.

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