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What’s the Best Jury Size?
What’s the Best Jury Size?

Slate; April 25, 2013

Several years ago, a man from Oregon named Alonso Alvino Herrera borrowed a friend’s car and never returned it. He was arrested and charged with unauthorized use of a vehicle and possession of stolen property. In 2008, a jury acquitted him of the second charge but convicted him of the first charge … by a 10-to-2 vote.

Does something strike you as odd about this story? Isn’t a verdict in a criminal trial supposed to be unanimous? The answer is yes in 48 states and yes if the case is tried in a federal court. But two states, Oregon and Louisiana, allow convictions by a nonunanimous vote. Oregon allows a 10-to-2 vote in noncapital cases; Louisiana’s threshold for conviction is 9 to 3. Arguably, Herrera had to go to jail for the crime of living in Oregon.

The Supreme Court has allowed this conflict between federal and state law (as well as between state law and conventional wisdom) to persist for more than 40 years, during which time it has come up with a mishmash of seemingly arbitrary rules about what constitutes a legal trial. A jury of six, the Supreme Court has decided, is constitutional (Williams v. Florida, 1970). A jury of five, however, is not constitutional (Ballew v. Georgia, 1978). In a jury of six, conviction must be unanimous (Burch v. Louisiana, 1979). But in a jury of 12, conviction does not have to be unanimous (Johnson v. Louisiana and Apodaca v. Oregon, 1972).

The Supreme Court’s rationale has been as confusing as its decisions. “The line between five- and six-member juries is difficult to justify, but a line has to be drawn somewhere,” wrote Justice Lewis Powell in Ballew v. Georgia. Justice Harry Blackmun, in the majority opinion for that case, cited several studies by social scientists on the error rate of juries of different sizes and wrote in a footnote: “We have considered [these studies] carefully because they provide the only basis, besides judicial hunch, for a decision about whether smaller and smaller juries will be able to fulfill the purpose and functions of the Sixth Amendment.” Powell, though agreeing with the decision, chastised Blackmun’s justification: “I have reservations as to the wisdom—as well as the necessity—of Mr. Justice Blackmun’s heavy reliance on numerology derived from statistical studies.”

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