Judging the Jury Vote
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Policy Apr 7, 2007

Judging the Jury Vote

Explaining the pitfalls of total agreement

Based on the research of

Timothy Feddersen

Wolfgang Pesendorfer

The Sixth Amendment to the Bill of Rights states that in criminal court cases defendants shall enjoy the right to trial by an “impartial jury of the State.” Today, the unanimous vote helps courts to abide by American ideals. Clearly, if any juror has a doubt about a defendant’s guilt, the unanimity rule will protect the subject from wrongful punishment, right?

Maybe not.

This is a possibility that Kellogg School professor Timothy Feddersen came across in his research, which suggests that during unanimous elections, people may have an incentive to vote strategically, in a way that produces unfavorable outcomes.

At the annual Kellogg Oh Be Joyful faculty and staff dinner in June, Feddersen received the inaugural Stanley Reiter Best Paper Award, established to recognize outstanding research published by a faculty member in the preceding four calendar years, for his paper “Convicting the Innocent: The Inferiority of Unanimous Jury Verdicts” (with Wolfgang Pesendorfer), printed in the American Political Science Review (vol. 92, no. 1). To understand the theory, he explains, one must understand that each person has private information that is relevant to other jurors’ decisions as well.

“If people voted naively, without knowing information that others may know, under unanimity rule guilty people would almost always be acquitted,” notes Feddersen, the Wendell Hobbs Professor of Managerial Economics and Decision Sciences.

Unlike majority rule, in which a vote is pivotal if the other voters equally split their votes between the two alternatives, a vote in a unanimous election is pivotal only if other voters have all voted the same way.

“If my vote is pivotal it is because everyone else has voted to convict,” Feddersen explains. “If I believe everyone else is voting on the basis of private information not available to me, then I may reason that I should not vote to acquit even when I believe the defendant to be innocent, thus effectively delegating the group’s decision from me, with my limited information, to the group.”

Unanimity rule therefore creates “perverse incentives” for jurors that may lead to higher probabilities of both acquitting guilty defendants and convicting innocent ones, than if a rule such as simple majority had been used, Feddersen contends.

Additionally, this reasoning could be mutual among voters, so increasing the size of the jury could actually increase the probability of convicting an innocent defendant.

Since 1994, Feddersen has worked with Pesendorfer, examining strategic voting in elections. In 1997, they published a paper arguing that a wide variety of voting rules are successful when voting strategically. Feddersen says the research on the unanimity rule came to mind as an afterthought.

“When this research started, we weren’t interested in different voting rules; we were more interested in participation in elections, the way elections aggregate information, and the incentive for people to participate in elections,” he explains.

Feddersen’s work is the first to consider the effect of strategic voting on the unanimity rule, and preliminary experiments have supported the theory’s predictions. Nevertheless, he cautions that the theory is not a recommendation for reform.

“This is an abstract mathematical model and not a claim about how people actually reason. We don’t have much to say about how people actually make decisions, only that they will have an incentive to act in a particular way. There are a number of factors that get in the way of immediately going from this paper to saying we ought to get rid of the unanimous jury verdict,” he says.

For example, he notes, his paper does not consider the process of jury deliberation. What if people talk to one another before they decide? Then the voting rule wouldn’t matter because there is no private information, he points out. Then too, what if people have other motivations?

Feddersen is looking to answer some of these questions in his present research on the impact that ethically minded voters may have on models of deliberation. “I’m interested in what kinds of incentives different voting rules create for people to talk,” he says.

“It appears that voting by unanimity rule doesn’t promote discussion as well as some people have thought.”

Featured Faculty

Wendell Hobbs Professor of Managerial Politics; Professor of Managerial Economics & Decision Sciences; Chair of Personnel Committee

About the Writer
Susannah Chen, freelance writer. Article featured originally in Kellogg World, Winter 2002
About the Research
Feddersen, Tim and Wolfgang Pesendorfer (1998). "Convicting the Innocent: The Inferiority of Unanimous Jury Verdicts," American Political Science Review, 92(1): 23-35.

This article received the Kellogg School's "Stanley Reiter Best Paper Award" in 2002.
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