Comparing Categorical and Probabilistic Fingerprint Evidence

Fingerprint examiners traditionally express conclusions in categorical terms, opining that impressions do or do not originate from the same source. Recently, probabilistic conclusions have been proposed, with examiners estimating the probability of a match between recovered and known prints. This study presented a nationally representative sample of jury‐eligible adults with a hypothetical robbery case in which an examiner opined on the likelihood that a defendant\u27s fingerprints matched latent fingerprints in categorical or probabilistic terms. We studied model language developed by the U.S. Defense Forensic Science Center to summarize results of statistical analysis of the similarity between prints. Participant ratings of the likelihood the defendant left prints at the crime scene and committed the crime were similar when exposed to categorical and strong probabilistic match evidence. Participants reduced these likelihoods when exposed to the weaker probabilistic evidence, but did not otherwise discriminate among the prints assigned different match probabilities

Identifying fingerprint expertise

“CSI”-style TV shows give the impression that fingerprint identification is fully automated. In reality, when a fingerprint is found at a crime scene, it is a human examiner who is faced with the task of identifying the person who left the print—a task that falls squarely in the domain of psychology. The difficulty is that no properly controlled experiments have been conducted on fingerprint examiners’ accuracy in identifying perpetrators (Loftus & Cole, 2004), even though fingerprints have been used in criminal courts for more than 100 years. Examiners have even claimed to be infallible (Federal Bureau of Investigation, 1984). However, the U.S. National Academy of Sciences has recently condemned these claims as scientifically implausible, reporting that faulty analyses may be contributing to wrongful convictions of innocent people (National Research Council, Committee on Identifying the Needs of the Forensic Science Community, 2009). Proficiency tests of fingerprint examiners and previous studies of examiners’ performance have not adequately addressed the issue of accuracy, and they been heavily criticized for (among other things) failing to include large, counterbalanced samples of targets and distractors for which the ground truth is known (see Cole, 2008, and Vokey, Tangen, & Cole, 2009). Thus, it is not clear what these tests say about the proficiency of fingerprint examiners, if they say anything at all. Researchers at the National Academy of Sciences and elsewhere (e.g., Saks & Koehler, 2005; Spinney, 2010) have argued that there is an urgent need to develop objective measures of accuracy in fingerprint identification. Here we present such data