The low prevalence effect in fingerprint comparison amongst forensic science trainees and novices

Abstract

The low prevalence effect is a phenomenon whereby target prevalence affects performance in visual search (e.g., baggage screening) and comparison (e.g., fingerprint examination) tasks, such that people more often fail to detect infrequent target stimuli. For example, when exposed to higher base-rates of ‘matching’ (i.e., from the same person) than ‘non-matching’ (i.e., from different people) fingerprint pairs, people more often misjudge ‘non-matching’ pairs as ‘matches’–an error that can falsely implicate an innocent person for a crime they did not commit. In this paper, we investigated whether forensic science training may mitigate the low prevalence effect in fingerprint comparison. Forensic science trainees (n = 111) and untrained novices (n = 114) judged 100 fingerprint pairs as ‘matches’ or ‘non-matches’ where the matching pair occurrence was either high (90%) or equal (50%). Some participants were also asked to use a novel feature-comparison strategy as a potential attenuation technique for the low prevalence effect. Regardless of strategy, both trainees and novices were susceptible to the effect, such that they more often misjudged non-matching pairs as matches when non-matches were rare. These results support the robust nature of the low prevalence effect in visual comparison and have important applied implications for forensic decision-making in the criminal justice system.

Interpol review of fingermarks and other body impressions (2019 – 2022)

“…Numerous studies aimed at understanding the cognitive and perceptual processes involved in fingerprint visual comparison tasks. They served to demonstrate (a) the benefit of perceptual training based on statistically rare features [ 84 ]; (b) the existence of a reliable visual comparison ability by experts compared to novices [ 85 ]; (c) the existence of a prevalence effect in the sense that experts and novices alike more often misjudged non-matching pairs as “matches” when non-matches were rare [ 86 ]; (d) the benefit of distributing decisions to groups of raters who independently assess the same information [ 87 ], in other words adopting a truly blind verification process; (e) the efficiency of fingerprint experts at locating specific targets on fingerprint images compared to novices, hence testifying to a domain-specific expertise [ 88 ] (f) empirical evidence that lineups (i.e. embedding the corresponding person of interest's prints among known non-source prints); promoted conservative decision-making [ 89 ].…”

On the (mis)calculation of forensic science error rates

“…Although the authors use reproducibility data to argue that verification would detect many such errors, their methodology assumes universal and blind verification, which is ideal but rare in practice ( 8 , 9 ). Moreover, false positive errors (whether definitive or qualified) were not limited to a subset of samples or examiners; they occurred for 87% of nonmated sets (89/102) and among 89% of examiners who judged at least 40 nonmated sets (57/64).…”