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                            Library & Multimedia
 Validity of forensic cartridge-case comparisons
NCJ Number
              306763
Journal

*PNAS* Volume: 120 Issue: 20 Dated: 2023
Author(s)
          Max Guyll;
                        Stephanie Madon;
                        Yueran Yang;
                        Gary Wells
Date Published

May 2023
Length
              9 pages
Annotation
              This article presents findings from a research project that evaluated the validity and probative value of cartridge-case comparisons.
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. (Published Abstract Provided)
      
  
          Additional Details
Grant Number(s)
        2014-DNR-4918


  
  
        
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        NIJ-Sponsored


  
  
        
  Publication Type
        Research (Applied/Empirical)


  
  
        
  Award
        Interagency Collaboration to Support Forensic Science Research
    
  
  
Date Published: May 1, 2023
    
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