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. 2023 May 16;120(20):e2210428120.
doi: 10.1073/pnas.2210428120. Epub 2023 May 8.

Validity of forensic cartridge-case comparisons

Max Guyll  1 , Stephanie Madon  1 , Yueran Yang  2 , Kayla A Burd  3 , Gary Wells  4
Affiliations

Validity of forensic cartridge-case comparisons

Max Guyll et al. Proc Natl Acad Sci U S A. .

Abstract

This article presents key findings from a research project that evaluated the validity and probative value of cartridge-case comparisons under field-based conditions. Decisions provided by 228 trained firearm examiners across the US showed that forensic cartridge-case comparison is characterized by low error rates. However, inconclusive decisions constituted over one-fifth of all decisions rendered, complicating evaluation of the technique's ability to yield unambiguously correct decisions. Specifically, restricting evaluation to only the conclusive decisions of identification and elimination yielded true-positive and true-negative rates exceeding 99%, but incorporating inconclusives caused these values to drop to 93.4% and 63.5%, respectively. The asymmetric effect on the two rates occurred because inconclusive decisions were rendered six times more frequently for different-source than same-source comparisons. Considering probative value, which is a decision's usefulness for determining a comparison's ground-truth state, conclusive decisions predicted their corresponding ground-truth states with near perfection. Likelihood ratios (LRs) further showed that conclusive decisions greatly increase the odds of a comparison's ground-truth state matching the ground-truth state asserted by the decision. Inconclusive decisions also possessed probative value, predicting different-source status and having a LR indicating that they increase the odds of different-source status. The study also manipulated comparison difficulty by using two firearm models that produce dissimilar cartridge-case markings. The model chosen for being more difficult received more inconclusive decisions for same-source comparisons, resulting in a lower true-positive rate compared to the less difficult model. Relatedly, inconclusive decisions for the less difficult model exhibited more probative value, being more strongly predictive of different-source status.

Keywords: cartridge-case comparisons; forensic examination; inconclusive decisions; probative value; validity.

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Conflict of interest statement

The authors declare no competing interest.

Figures

Fig. 1.
Fig. 1.
Decisions’ prediction of ground-truth status for Beretta 92FS.
Fig. 2.
Fig. 2.
Decisions’ prediction of ground-truth status for HiPoint C9.
See this image and copyright information in PMC

References

    1. National Research Council, Strengthening forensic science in the United States: A path forward (National Academies Press, 2009).
    1. Holdren J. P., Lander E. S., Press W., Savitz M. “Forensic science in criminal courts: Ensuring scientific validity of feature-comparison methods” (President’s Committee of Advisors on Science and Technology, 2016).
    1. Durose M. R., Burch A. M. “Publicly funded forensic crime laboratories: Resources and services, 2014”. Report NCJ 250151. (Bureau of Justice Statistics, 2016).
    1. Hamby J. E., Norris S., Petraco N. D. K., Evaluation of GLOCK 9 mm firing pin aperture shear mark individuality based on 1,632 different pistols by traditional pattern matching and IBIS pattern recognition. J. Foren. Sci. 61, 170–176 (2016). - PubMed
    1. AFTE Criteria for Identification Committee, Theory of identification, range striae comparison reports and modified glossary definitions. AFTE J. 24, 336–340 (1992).

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