How Jurors Evaluate Fingerprint Evidence: The Relative Importance of Match Language, Method Information, and Error Acknowledgment

Abstract

Fingerprint examiners use a variety of terms and phrases to describe a finding of a match between a defendant's fingerprints and fingerprint impressions collected from a crime scene. Despite the importance and ubiquity of fingerprint evidence in criminal cases, no prior studies examine how jurors evaluate such evidence. We present two studies examining the impact of different match phrases, method descriptions, and statements about possible examiner error on the weight given to fingerprint identification evidence by laypersons. In both studies, the particular phrase chosen to describe the finding of a match-whether simple and imprecise or detailed and claiming near certainty-had little effect on participants' judgments about the guilt of a suspect. In contrast, the examiner admitting the possibility of error reduced the weight given to the fingerprint evidence-regardless of whether the admission was made during direct or cross-examination. In addition, the examiner providing information about the method used to make fingerprint comparisons reduced the impact of admitting the possibility of error. We found few individual differences in reactions to the fingerprint evidence across a wide range of participant variables, and we found widespread agreement regarding the uniqueness of fingerprints and the reliability of fingerprint identifications. Our results suggest that information about the reliability of fingerprint identifications will have a greater impact on lay interpretations of fingerprint evidence than the specific qualitative or quantitative terms chosen to describe a fingerprint match.

The impact of proficiency testing information and error aversions on the weight given to fingerprint evidence

“…Finally, we examined general views on the reliability of fingerprint and DNA evidence. Consistent with prior research (Garrett & Mitchell, ), we found that the great majority of respondents believed that each individual's fingerprints are unique (1,222, or 84.3%) or are probably unique (189, or 13%), while only a few believed they that fingerprints are not individually unique (39, or 2.7%). A slightly smaller majority also believed that each individual's DNA is unique (1,188, or 81.9%) or is probably unique (173, or 11.9%), while a few believed an individual's DNA is not unique (89, or 6.1%).…”

“…In prior research, we found that a fingerprint examiner's admission that fingerprint identifications were sometimes erroneous and that his own identification opinion in the case at hand might be in error significantly reduced the weight given to fingerprint evidence in a criminal trial (Garrett & Mitchell, ). This result held whether the fingerprint expert raised the possibility of error during direct testimony or conceded that possibility on cross‐examination.…”

“…The fingerprint examiner issued a report concluding that: “A fingerprint recovered from the gun matched the right thumb of the defendant.” As is common within mock juror studies (e.g., McQuiston‐Surrett & Saks, ; Schklar & Diamond, ; Scurich & John, ; Thompson et al, ), we intentionally kept the case description simple and focused on the fingerprint evidence to avoid possible bolstering of the fingerprint evidence through other corroborating evidence (corroborating evidence can lend credibility to the fingerprint identification and allay any concerns potential jurors may have about the reliability of the fingerprint evidence). Furthermore, although fingerprint examiners employ a variety of terms to indicate source identification (see Table in Garrett & Mitchell, ), we chose one of the simpler formulations, using “match” terminology to avoid the need for an extended discussion of the expert's testimony and because the different formulations tend to produce the same results (Garrett & Mitchell, ; see also Kadane & Koehler, ).…”

“…indicate source identification (see Table 1 in Garrett & Mitchell, 2013), we chose one of the simpler formulations, using "match" terminology to avoid the need for an extended discussion of the expert's testimony and because the different formulations tend to produce the same results (Garrett & Mitchell, 2013; see also Kadane & Koehler, 2018).…”

Comparing Categorical and Probabilistic Fingerprint Evidence

“…In prior research, we found that the particular categorical language used by fingerprint examiners mattered little: Categorical match opinions carried considerable weight regardless of whether the examiner stated that opinion starkly, bolstered it with unwarranted statements of certainty, or qualified it by admitting that someone other than the defendant might be the source of the latent prints . This prior research did not examine, however, whether the subjective probabilities of a match, as determined by an examiner, corresponded to the jurors’ assigned probabilities.…”