Date of Award

Spring 5-8-2023

Document Type


Degree Name

Master of Arts (MA)


Forensic Psychology



First Advisor or Mentor

Margaret Bull-Kovera

Second Reader

Jacqueline Katzman

Third Advisor

Steven Penrod


Eyewitness misidentification is a leading cause of wrongful conviction. Although the prior probability of guilt (i.e., pre-identification evidence strength) is the most important factor for predicting a defendant’s actual guilt status and the accuracy of any subsequent eyewitness identification, no study has examined whether it affects juror decisions. This oversight is problematic because when officers place suspects in lineups when there is little evidence connecting them to the crime, it falls on jurors to examine the probative value of identification evidence. Participants (N = 357) watched a mock trial depicting an armed robbery that varied pre-identification evidence (strong vs. weak), and whether the expert witness testified about the importance of base-rates of guilt (present, not present). I predicted that when there is expert testimony on the importance of the base rate of guilty suspects in identification procedures, participants will be more sensitive to variations in the strength of the evidentiary connection between the defendant and the crime prior to the positive identification. Expert testimony on the importance of base rates of guilt did not affect participant judgments, but it did cause participants to be more skeptical of lineup fairness regardless of the strength of the evidence connecting the suspect to the crime. Overall, participants were sensitive to variations in the strength of the pre-identification evidence without the benefit of expert testimony; however, their judgments underestimated the likely accuracy of identifications made when the pre-identification connection between the suspect and the crime was strong. Thus, as expert testimony is not sufficient for helping jurors evaluate the probability of a suspect’s guilt post-identification, it will be important to implement procedures that will ensure that the base rate of guilty suspects in identification procedures is high enough to produce a sufficient probability of guilt after a positive identification, like a departmental requirement of evidence-based suspicion.



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