New study shows how often juries get it wrong

From a Northwestern University press release (28 June):

…A new Northwestern University study shows that juries in criminal cases many times are getting it wrong. In a set of 271 cases from four areas, juries gave wrong verdicts in at least one out of eight cases, according to “Estimating the Accuracy of Jury Verdicts,” a paper by a Northwestern University statistician that is being published in the July issue of Journal of Empirical Legal Studies.

“Contrary to popular belief, this study strongly suggests that DNA or other after-the-fact evidence is not the only way to know how often jury verdicts are correct,” said Bruce Spencer, the study’s author, professor of statistics and faculty fellow at the Institute for Policy Research at Northwestern. “Based on findings from a limited sample, I am optimistic that larger, carefully designed statistical studies would have much to tell us about the accuracy of jury verdicts.”

Spencer cautions that the numerical findings should not be generalized to broader sets of cases, for which additional study would be needed, but the study strongly suggests that jury verdicts can be studied statistically. If such studies were conducted on a large scale, they might lead to better understanding of the prevalence of incorrect verdicts — false convictions and false acquittals, he said.

The rest of the press release gives some more details on this somewhat complex method, or you can download the paper from the link below.

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