Do Jurors Give Appropriate Weight to Forensic Identification Evidence?


  • William C. Thompson,

  • Suzanne O. Kaasa,

  • Tiamoyo Peterson

  • The research reported here was supported by National Science Foundation Grant No. SES-0617672. The authors thank Mr. Alan Carlson, Chief Executive Officer and Jury Commissioner of the Superior Court of Orange County, California, and his staff, for their assistance in completing this research.

Address correspondence to William C. Thompson, Department of Criminology, Law & Society, University of California, Irvine, CA 92617; email:


Do jurors give appropriate weight to forensic identification evidence? When judging the value of forensic evidence, are they sensitive to the probability of a false match? To answer these questions, we conducted two jury simulation experiments—the first with undergraduate participants, the second with members of a county jury pool. The experiments examined the weight that participants gave to forensic DNA evidence relative to Bayesian norms when evaluating a hypothetical criminal case. We found that aggregate judgments were generally consistent with Bayesian expectations, although people overvalued the DNA evidence when the probability of a false report of a match was high relative to the random match probability. Judgments of the chances the defendant was guilty varied appropriately in response to the variation in the probability of a false report of a match, as did verdicts. Our findings refute claims that jurors are always conservative Bayesians when evaluating forensic evidence and suggest, instead, that they use a variety of judgmental strategies and sometimes engage in fallacious statistical reasoning. In light of these findings, we identify circumstances in which forensic evidence may be overutilized, discuss implications for legal policy, and suggest additional lines of research.