The Effects of Cognitive Bias, Examiner Experience, and Stimulus Material on Forensic Evidence Analysis

Forensic examiners have come under scrutiny in recent years because of high profile exoneration cases that have highlighted the negative impact contextual bias can have on investigations including forensic evidence analyses. This has led to several proposed solutions to reduce the effects of bias including blind testing and redacting task-irrelevant information. However, practitioners have not been receptive to such recommendations because of the limitations found in past research, such as the use of untrained undergraduate students to examine complex pieces of forensic evidence (e.g., fingerprints). The current study thus had the following aims: (a) examine the effect of contextual bias on examiners’ evaluation of forensic evidence by varying the amount of pre-comparison information available to participants, (b) compare novice and expert examiners’ performance when conducting forensic analyses and their vulnerabilities to contextual bias, and (c) investigate the effect of contextual bias on examiners’ evaluation of different types of forensic evidence. Expert forensic examiners and novice undergraduate students were recruited and provided with a lab analysis request form that either contained all case summary details about a mock crime, no case summary details about the crime (i.e., blind testing) or had task-irrelevant case summary details redacted. Participants were asked to compare matching and non-matching fingerprint and footwear impression evidence. Results suggest no effect of blinding examiners from case information or redacting task-irrelevant information on examiners’ decisions. Findings also suggest that both examiner experience and the type of forensic evidence analyzed can have a significant effect on examiners’ judgments. Expert examiners were significantly more accurate than novices. However, expert examiners were only significantly more accurate and better able to discriminate between matching and non-matching pairs of evidence when analyzing fingerprint evidence and not footwear impression evidence. These findings suggest caution when using forensic stimuli with novice samples to investigate cognitive bias in forensic examination. Finally, the present study suggest that the proposed blinding and redaction procedures require additional research including expert examiners and a spectrum of forensic stimulus material to yield measurable effects of cognitive bias