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Saul M. Kassin

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Over a century of basic cognitive and social psychological research shows that humans naturally seek out, perceive, and interpret evidence in ways that serve to validate their prevailing beliefs (i.e., confirmation bias; Nickerson, 1998). In criminal justice settings, a priori beliefs regarding the guilt or innocence of a suspect can likewise guide the collection, interpretation, and appraisal of evidence in a self-verifying manner (i.e., forensic confirmation bias; Kassin, Dror, & Kukucka, 2013). Recently, confirmation bias has been implicated as a source of forensic science errors in wrongful conviction cases (e.g., National Academy of Sciences, 2009; Risinger, Saks, Rosenthal, & Thompson, 2002). Accordingly, many have suggested procedural reforms to mitigate the detrimental impact of unconscious bias on judgments of forensic evidence.

Three studies tested the effects of exposure to case information and evidence lineup use on judgments of handwriting evidence in a mock investigation. In Studies 1 and 2, participants who were aware of a suspect's confession rated non-matching handwriting samples from the suspect and perpetrator as more similar to each other, and were more likely to misjudge them as having been authored by the same individual. The findings of Studies 1 and 2 thus further raise growing concerns over allowing forensic science examiners access to case information that can unwittingly produce confirmation bias and result in erroneous judgments.

In Study 2, the use of a simultaneous evidence lineup increased choosing rates relative to an evidence "showup," and produced a corresponding decrease in judgment accuracy. In Study 3, sequential evidence lineups dramatically reduced false identifications relative to simultaneous lineups, without causing a significant reduction in correct identifications. By showing parallel effects between forensic evidence lineup identification and eyewitness lineup identification, Studies 2 and 3 suggest the potential value of evidence lineups as a means of protecting against bias and reducing systematic error in judgments of forensic evidence.

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