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Jurors' Perceptions of the Probative Value of Non-Identifications


There is considerable evidence that jurors attribute significant weight to testimony in which an eyewitness makes a positive identification. By contrast, little empirical research has been conducted on how jurors perceive non-identifications, which is when an eyewitness affirmatively states that the defendant is not the perpetrator. Using a mock juror paradigm, three experiments tested whether jurors are sensitive to non-identification testimony by recruiting participants through Amazon Mechanical Turk. Participants in Study 1 (N = 163) read a court case where the eyewitness identification evidence was manipulated (positive identification vs. non-identification vs. no eyewitness identification evidence). Participants were no more likely to acquit the defendant when presented with non-identification testimony compared to a case that had no eyewitness testimony at all. Study 2 tested one possible explanation for why mock jurors gave no apparent weight to the non-identification: because there was no explanation or elaboration for the non-identification. In Study 2, participants (N = 220) read the same court case and all received non-identification testimony, but the reason surrounding a non-identification decision was manipulated: uninformative explanation (“I know what I saw and I know it’s not the guy”) or informative explanation (“the man I saw had blonde hair and everyone in the lineup had brown hair”) or no explanation provided. The data revealed that an informative explanation reduced conviction rates by half compared to the other conditions, suggesting that jurors have difficulty utilizing the non-identification evidence, unless it is accompanied by an informative explanation.

Study 3 (N = 642) tested the possibility that how jurors evaluate a non-identification is contingent upon how it relates to other evidence in the case as a whole. Based on the phenomena of confirmation bias, it was hypothesized that jurors will accord the non-identification testimony little weight when the case evidence is strong (hence the non-identification is inconsistent with the other case evidence) and relatively more weight when the case evidence is weak (hence the non-identification is consistent with the other case evidence). Study 3 manipulated the strength of the case (strong vs. moderate vs. weak) and the type of eyewitness testimony (positive identification vs. non-identification). In addition to the eyewitness testimony, an expert witness testified about the probative value of the eyewitness identification/non-identification to provide a normative benchmark against which to compare jurors’ responses. The data revealed that jurors engage in confirmation bias in the direction hypothesized, whereby the positive identification was accorded more weight when the other case evidence was strong compared to weak, and a non-identification was accorded more weight when the other case evidence was weak relative to strong. The fact that jurors’ evaluation of the eyewitness identification—regardless of type—depended on unrelated case evidence (e.g., repaying a debt to his credit card company) is non-normative.

Taken as a whole, these studies suggest that mock jurors do not intuitively ascribe much value to non-identifications, though they do so when there is an elaborate and plausible explanation for the non-identification and if the other case evidence is weak. Directions for future research and implications of these findings for policy are discussed.

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