Validity of forensic cartridge-case comparisons

Proceedings of the National Academy of Sciences, Journal Year: 2023, Volume and Issue: 120(20)

Published: May 8, 2023

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

Language: Английский

---

The Hawthorne effect in studies of firearm and toolmark examiners

Journal of Forensic Sciences, Journal Year: 2025, Volume and Issue: unknown

Published: April 10, 2025

Abstract The Hawthorne effect refers to the tendency of individuals behave differently when they know are being studied. In forensic science domain, concerns have been raised about “strategic examiner,” where examiner uses different decision thresholds depending on whether in a test situation or working an actual case. blind testing conducted by Houston Forensic Science Center (“HFSC”) firearms examination presents unique opportunity hypothesis that rate inconclusive calls differs for discovered vs. undiscovered tests firearm examination. Over 5 years, 529 item comparisons were filtered into casework at HFSC. items was 56.4%, while 39.3%. Thus, percentage 43.5% higher among than items. This pattern results held bullet (83% 59%) and cartridge case (29% 20%) both same‐source different‐source comparisons. These findings corroborate examiners tested demonstrate necessity if research goal is evaluate performance conducting casework.

Language: Английский

---

The scientific reinvention of forensic science

Proceedings of the National Academy of Sciences, Journal Year: 2023, Volume and Issue: 120(41)

Published: Oct. 2, 2023

Forensic science is undergoing an evolution in which a long-standing "trust the examiner" focus being replaced by scientific method" focus. This shift, progress and still partial, critical to ensure that legal system uses forensic information accurate valid way. In this Perspective, we discuss ways move more empirically grounded culture for sciences impacts testing, error rate analyses, procedural safeguards, reporting of results. However, caution ultimate success reinvention likely depends on whether courts begin engage with claims rigorous

Language: Английский

---

Shifting decision thresholds can undermine the probative value and legal utility of forensic pattern-matching evidence

Proceedings of the National Academy of Sciences, Journal Year: 2023, Volume and Issue: 120(41)

Published: Oct. 2, 2023

Forensic pattern analysis requires examiners to compare the patterns of items such as fingerprints or tool marks assess whether they have a common source. This article uses signal detection theory model examiners' reported conclusions (e.g., identification, inconclusive, exclusion), focusing on connection between examiner's decision threshold and probative value forensic evidence. It Bayesian network explore how shifts in thresholds may affect rates ratios true false convictions hypothetical legal system. demonstrates that small thresholds, which arise from contextual bias, can dramatically pattern-matching evidence its utility

Language: Английский

---

Forensic comparison of fired cartridge cases: Feature-extraction methods for feature-based calculation of likelihood ratios

Forensic Science International Synergy, Journal Year: 2022, Volume and Issue: 5, P. 100272 - 100272

Published: Jan. 1, 2022

We describe and validate a feature-based system for calculation of likelihood ratios from 3D digital images fired cartridge cases. The includes database the bases 10 cartridges per firearm approximately 300 firearms same class (semi-automatic pistols that fire 9 mm diameter centre-fire Luger-type ammunition, have hemispherical firing pins parallel breech-face marks). were captured using Evofinder®, an imaging is commonly used by operational forensic laboratories. A key component research reported comparison different feature-extraction methods. Feature sets compared include those previously proposed in literature, plus Zernike-moment based features. Comparisons are also made feature extracted firing-pin impression, region, whole region interest (firing-pin impression + flowback if present). Likelihood calculated statistical modelling pipeline standard voice comparison. Validation conducted results assessed validation procedures metrics graphics

Language: Английский

---

Scientific guidelines for evaluating the validity of forensic feature-comparison methods

Proceedings of the National Academy of Sciences, Journal Year: 2023, Volume and Issue: 120(41)

Published: Oct. 2, 2023

When it comes to questions of fact in a legal context-particularly about measurement, association, and causality-courts should employ ordinary standards applied science. Applied sciences generally develop along path that proceeds from basic scientific discovery some natural process the formation theory how works what causes fail, development an invention intended assess, repair, or improve process, specification predictions instrument's actions and, finally, empirical validation determine instrument achieves effect. These elements are salient deeply embedded cultures medicine engineering, both which primarily grew sciences. However, inventions underlie most forensic science disciplines have few roots science, they do not sound theories justify their predicted results tests prove work as advertised. Inspired by "Bradford Hill Guidelines"-the dominant framework for causal inference epidemiology-we set forth four guidelines can be used establish validity comparison methods generally. This is checklist establishing threshold minimum validity, no magic formula determines when particular hypotheses passed necessary threshold. We illustrate these considering discipline firearm tool mark examination.

Language: Английский

---

Three-Way ROCs for Forensic Decision Making

Statistics and Public Policy, Journal Year: 2023, Volume and Issue: 10(1)

Published: July 21, 2023

Firearm examiners use a comparison microscope to judge whether bullets or cartridge cases were fired by the same gun. Examiners can reach one of three possible conclusions: Identification (a match), Elimination (not Inconclusive. Numerous error rate studies report that firearm commit few errors when they conduct these examinations. However, also many inconclusive judgments (>50%), and how score responses is controversial. There have recently been Signal Detection Theory (SDT) primers in this domain. Unfortunately, analyses rely on hypothetical data fail address response issue adequately. This article reports an SDT analysis using from large study practicing examiners. First, we demonstrate problem relying traditional two-way model, which either drops combines responses; addition lacking ecological validity, approach leads implausible results. Second, introduce readers three-way model. We forensic firearms While statistically complicated, it well suited evaluate performance for any domain decision categories exist.

Language: Английский

---

The use and abuse of the elusive construct of inconclusive decisions

Law Probability and Risk, Journal Year: 2022, Volume and Issue: 21(1), P. 85 - 87

Published: March 1, 2022

Inconclusives1 is an elusive conclusion in any domain, and particular the forensic sciences. Until recently, it has been relatively neglected, if not ignored, as viewed incorrectly a 'non-decision' with little implication or importance (in contrast to decisive conclusion, e.g., 'match' vs. 'exclusion', 'homicide' 'accident'). However, inconclusives simply matter of 'not decide', but actually involves making important decision 'decide decide' (Dror Langenburg, 2019). Inconclusive decisions have critical implications casework error rate studies. In casework, fingerprinting, deciding inconclusive rather than exclusion may prevent police from eliminating suspect investigation. pathology, that death undetermined homicide full This be especially problematic there systematic disproportional conclusions when people die while custody.

Language: Английский

---

Authors' response to Gutierrez et al Commentary on

Journal of Forensic Sciences, Journal Year: 2023, Volume and Issue: 68(3), P. 1102 - 1104

Published: April 21, 2023

Language: Английский

---