Rating the Performance of Diverse Juries: A Scientific Perspective

The subject of diversity often elicits strong, entrenched ideological opinions. But Sam Sommers, an associate professor of psychology at Tufts University, is more intrigued by the facts—what can be noted, objectively, about diversity’s impact? Through his work as an experimental psychologist, Dr. Sommers explores issues related to stereotyping, prejudice, and group diversity.

Juries are among the groups he has researched. His 2006 study on how a jury’s deliberations are impacted by its racial composition remains one of few on this particular topic. He recently discussed that study, its findings, and its limitations. A condensed version of the conversation follows.

Q. How was the study conducted?

Professor Sommers: Using mostly participants who showed up for jury duty in Washtenaw County, Mich. — and a smaller group who responded to newspaper ads in the same area — we recruited mock six-person juries. Fifteen of these were all-white, and 15 were mixed, defined here as having four white and two black jurors. Participants were shown the videotaped one-day criminal trial of a black defendant, and then observed during their deliberations.

Q. Why were there no all-black mock juries?

Professor Sommers: Ideally, there would have been, but there were practical constraints. Our arrangement with the court required that we not alter the demographics of the jurors who remained after we chose our participants. So, the proportion of black participants in our study was as high as permissible.

Q. What did you observe about the effect of racial diversity on the decision making process of the juries?

Professor Sommers: We found that the racially diverse juries made decisions in different ways. They raised a broader range of questions, made fewer factual errors, and were more willing to discuss and debate uncomfortable or controversial issues related to race.

Q. To what do you attribute these differences? 

Professor Sommers: Three factors. First, as other studies bear out, black jurors are generally less conviction-prone than white ones. So, prior to deliberations, when the preliminary vote was taken, the mixed juries had fewer voices arguing for a guilty verdict. Second, something informational was going on, meaning that having people from diverse backgrounds present yielded diverse opinions. People on the diverse juries were exposed to more information in their jury rooms. It’s important to note that this second factor is the one most people would assume leads to the difference—the fact that black jurors bring different perspectives to the group. But, the third factor is equally important: the white jurors thought differently when in mixed groups.

Q. Why was that?

Professor Sommers: Something more motivational was at play. Even before deliberations began, the white jurors on the mixed juries were less likely to vote guilty. In homogeneous groups, we sometimes operate on autopilot. But you think more carefully and have a different mindset in a diverse group.

Q. What questions are left open by the study?

Professor Sommers: First, in this study the defendant was black. It’s unclear if the effect would be as conclusive if the defendant were not. A white juror may be hyper-aware that he is going to be discussing a case about a black guy with black people. Second, we don’t know whether the same effects—less questioning, more errors, and less talk about racial issues—would have been observed among all-black juries. We don’t know if we’re seeing a generalized finding about homogeneous groups. Finally, we don’t know if the effects would be the same in a civil, as opposed to criminal, trial.

Q. Don’t lawyers just want what’s best for their client, even if that means a homogeneous jury that looks like and, arguably, identifies with their client?

Professor Sommers: We operate within an adversarial legal system, so what any individual attorney may want in terms of jury composition will depend on how favorably that jury is likely to view her client’s case. There is a tension between what an individual might want to accomplish and what we as a society want to accomplish. But we have to consider what’s better from a system-wide viewpoint. And from that perspective, I think we do want juries that think things through and question what they are told.

Professor Sommers is the author of Situations Matter, which explores the invisible forces that shape human behavior.