Statistics in the Jury Box: How Juror Respond to Mitochondial DNA Probabilities

Abstract:     
This article describes parts of an unusually realistic experiment on the comprehension of expert testimony on mitochondrial DNA (mtDNA) sequencing in a criminal trial for robbery. Specifically, we examine how jurors who responded to summonses for jury duty evaluated portions of videotaped testimony involving probabilities and statistics. Although some jurors showed susceptibility to classic fallacies in interpreting conditional probabilities, the jurors as a whole were not overwhelmed by a 99.98% exclusion probability that the prosecution presented. Cognitive errors favoring the defense were more prevalent than ones favoring the prosecution. These findings lend scant support to the legal argument that mtDNA evidence (with modest exclusion probabilities) should be excluded because jurors are prone to overvalue such evidence. The article also introduces a new method for inferring the perceived probability of guilt that satisfies the burden of persuasion for most jurors.

Keywords: jury, DNA, scientific evidence, probability fallacies

Accepted Paper Series