Quantifying the strength of palmprint comparisons: Majority identifications with surprisingly low value.

Friction ridge examiners report conclusions to palm impression comparisons similarly to fingerprint impression comparisons, although several key differences exist. These include an extensive search process in palm impressions, differences in minutiae rarity, and orientation challenges that most fingerprint comparisons do not require. Most US laboratories use a three-conclusion scale that includes Identification, Exclusion, and Inconclusive, which have not been calibrated against the actual strength of the evidence in palmprint comparisons. To measure the strength of the evidence of palmprint impressions, the present work constructs likelihood ratios using an ordered probit model based on distributions of examiner responses in an error rate study. Many likelihood ratios calculated are quite modest and the current articulation scales may overestimate the strength of support for same source propositions by up to five orders of magnitude. These likelihood ratios help calibrate the articulation language and may offer an alternative to categorical reporting scales.