In a perfect world, at every trial, the innocent would be acquitted, and the guilty would be convicted each time with perfect accuracy. Alas, it is not a perfect world. As statistics are now telling us, juries get it wrong many times.
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 Northwestern University statistician Bruce Spencer.
To conduct the study, Spencer analyzed jury verdicts, comparing decisions of actual jurors with decisions of judges who were hearing the cases they were deciding. In other words, as a jury was deliberating about a particular verdict, its judge filled out a questionnaire giving what he or she believed to be the correct verdict. "To assess the accuracy of jury verdicts, we need a second opinion of what the verdict should be," said Spencer.
An Imperfect Legal System
The agreement rate was only 77 percent - not the ideal 100 percent. With the assumption that judges are at least as accurate as jurors after completion of all testimony, we can get an estimate of jury accuracy that is likely to be higher than the actual accuracy. Thus, the 77 percent agreement rate means that juries are accurate up to 87 percent of the time or less, or reach an incorrect verdict in at least one out of eight cases.
"Some of the errors are incorrect acquittals, where the defendant goes free, and some are incorrect convictions," Spencer said. "As a society can we be satisfied if 10 percent of convictions are incorrect? Can we be satisfied knowing that innocent people go to jail for many years for wrongful convictions?"
By Neil Whitehall
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See the full report at http://www.northwestern.edu/ipr/publications/papers/2006/wp0605.pdf.