Validating strength‐of‐support conclusion scales for fingerprint, footwear, and toolmark impressions

Abstract

In the pattern comparison disciplines such as fingerprints, footwear, and toolmarks, the results of a comparison are communicated by examiners in the form of categorical conclusions such as Identification or Exclusion. These statements have been criticized as requiring knowledge of prior probabilities by the examiners and being overinterpreted by laypersons. Alternative statements based on strength‐of‐support language have been proposed. The current study compares traditional conclusion scales against strength‐of‐support scales to determine how these new statements might be used by examiners in casework. Each participant completed 60 comparisons within their discipline, which were designed to approximate casework conditions, using either a traditional or a strength‐of‐support conclusion scale. The scale used on each trial was randomly assigned, and participants knew the scale for that trial as they began the comparison. Fingerprint examiners were much less likely to use Extremely Strong Support for Common Source than Identification. Footwear examiners treated the traditional and strength‐of‐support scales similarly, but toolmark examiners were much less likely to use Extremely Strong Support for Common Source than Identification, similar to fingerprint examiners. A separate group of fingerprint examiners used Identification less often when an expanded scale was available. The results demonstrate that expanded scales may result in the highest conclusion category being used less often by examiners when other alternatives are possible, and the term “extremely strong support” may introduce risk aversion on the part of examiners.

Accuracy of comparison decisions by forensic firearms examiners

“…The participants in this study were directed to use the AFTE range of conclusions [ 46 ], which predominates in North America, to express their comparison decisions. Alternative scales, which describe conclusions in terms of strength of support, are under consideration [ 59 , 60 ]. If adopted by the community, the value of studies using the AFTE range will endure.…”

Retracted: Generalisability and stability of visual comparison ability

“…They completed all four tasks (described below; three visual comparison tasks and one divergent validity task) in a randomised order and completed all trials in each task in a randomised order (except for the HMT‐SF which participants completed in its set order). We selected artificial‐print comparison from the Novel Object‐Matching Test as the most predictive task of visual comparison performance (as in Growns et al, 2022) and two novel tasks adapted from Busey et al (2022): footwear and toolmark comparison.…”

“…Participants completed 56 toolmark comparison trials (28 match and 28 non-match) from Busey et al (2022; see middle panel of Figure 1).…”

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

“…According to them, the strengths of expanded conclusion scales outweigh the limitations, but care must be taken with their implementation. A further study contrasted fingerprint, toolmarks and footwear marks [ 100 ]. It confirmed that examiners become more risk-averse with expanded scales (both on the source identification and source exclusion) and conclusion statements that contains “extremely strong support” are reserved for comparisons with the highest amount of support.…”