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Jury Poker: In Criminal Trials, the Odds Aren’t Good

A landmark study has been published by Northwestern statistics professor Bruce Spencer offering statistical and empirical data on the accuracy of U.S. jury verdicts. His method involved comparing the decision of a jury with the decision of the judge hearing the case, accomplished by having the judge fill out a questionnaire during jury deliberations. The data pool consisted of 290 criminal cases in Los Angeles; Washington D.C.; Maricopa County, Ariz.; and the Bronx, from 2000 to 2001.

Spencer’s analysis suggests that juries render incorrect verdicts an estimated 15% of the time (with an estimated standard of error of +/- 4 points), while judges are wrong in 12% of verdicts (including both convictions and acquittals). For those trials involving incorrect convictions, the chances of mistake are even higher: 25% of innocent defendants put on trial were handed a conviction by juries, and 37% were convicted by judges. Guilty defendants, meanwhile, were or would have been set free 10% of the time by a jury and 13% of the time by a judge.

While Spencer cautioned that more data is needed before reaching broad conclusions about the accuracy of criminal trials, his findings certainly highlight the vagaries of our current judicial system (which we’ve touched on before). Not to mention provide a reason to look again toward Steve Landsburg‘s theory that juries should be paid for their time and penalized for incorrect verdicts.

(Hat tip: Jian Li.)