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Firearm examination: Examiner judgments and computer-based comparisons.

ABSTRACT: Forensic firearm examination provides the court of law with information about the source of fired cartridge cases. We assessed the validity of source decisions of a computer-based method and of 73 firearm examiners who compared breechface and firing pin impressions of 48 comparison sets. We also compared the computer-based method's comparison scores with the examiners' degree-of-support judgments and assessed the validity of the latter. The true-positive rate (sensitivity) and true-negative rate (specificity) of the computer-based method (for the comparison of both the breechface and firing pin impressions) were 94.4% and at least 91.7%, respectively. For the examiners, the true-positive rate was at least 95.3% and the true-negative rate was at least 86.2%. The validity of the source decisions improved when the evaluations of breechface and firing pin impressions were combined and for the examiners also when the perceived difficulty of the comparison decreased. The examiners were reluctant to provide source decisions for "difficult" comparisons even though their source decisions were mostly correct. The correlation between the computer-based method's comparison scores and the examiners' degree-of-support judgments was low for the same-source comparisons to negligible for the different-source comparisons. Combining the outcomes of computer-based methods with the judgments of examiners could increase the validity of firearm examinations. The examiners' numerical degree-of-support judgments for their source decisions were not well-calibrated and showed clear signs of overconfidence. We suggest studying the merits of performance feedback to calibrate these judgments.

SUBMITTER: Mattijssen EJAT

PROVIDER: S-EPMC7821150 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature

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Firearm examination: Examiner judgments and computer-based comparisons.

Mattijssen Erwin J A T EJAT Witteman Cilia L M CLM Berger Charles E H CEH Zheng Xiaoyu A XA Soons Johannes A JA Stoel Reinoud D RD

Journal of forensic sciences 20200924 1

Forensic firearm examination provides the court of law with information about the source of fired cartridge cases. We assessed the validity of source decisions of a computer-based method and of 73 firearm examiners who compared breechface and firing pin impressions of 48 comparison sets. We also compared the computer-based method's comparison scores with the examiners' degree-of-support judgments and assessed the validity of the latter. The true-positive rate (sensitivity) and true-negative rate ...[more]

PMID: 32970858

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Project description:PurposeEnsuring that examiners in different parallel circuits of objective structured clinical examinations (OSCEs) judge to the same standard is critical to the chain of validity. Recent work suggests examiner-cohort (i.e., the particular group of examiners) could significantly alter outcomes for some candidates. Despite this, examiner-cohort effects are rarely examined since fully nested data (i.e., no crossover between the students judged by different examiner groups) limit comparisons. In this study, the authors aim to replicate and further develop a novel method called Video-based Examiner Score Comparison and Adjustment (VESCA), so it can be used to enhance quality assurance of distributed or national OSCEs.MethodIn 2019, 6 volunteer students were filmed on 12 stations in a summative OSCE. In addition to examining live student performances, examiners from 8 separate examiner-cohorts scored the pool of video performances. Examiners scored videos specific to their station. Video scores linked otherwise fully nested data, enabling comparisons by Many Facet Rasch Modeling. Authors compared and adjusted for examiner-cohort effects. They also compared examiners' scores when videos were embedded (interspersed between live students during the OSCE) or judged later via the Internet.ResultsHaving accounted for differences in students' ability, different examiner-cohort scores for the same ability of student ranged from 18.57 of 27 (68.8%) to 20.49 (75.9%), Cohen's d = 1.3. Score adjustment changed the pass/fail classification for up to 16% of students depending on the modeled cut score. Internet and embedded video scoring showed no difference in mean scores or variability. Examiners' accuracy did not deteriorate over the 3-week Internet scoring period.ConclusionsExaminer-cohorts produced a replicable, significant influence on OSCE scores that was unaccounted for by typical assessment psychometrics. VESCA offers a promising means to enhance validity and fairness in distributed OSCEs or national exams. Internet-based scoring may enhance VESCA's feasibility.

Project description:BackgroundA potential problem of clinical examinations is known as the hawk-dove problem, some examiners being more stringent and requiring a higher performance than other examiners who are more lenient. Although the problem has been known qualitatively for at least a century, we know of no previous statistical estimation of the size of the effect in a large-scale, high-stakes examination. Here we use FACETS to carry out a multi-facet Rasch modelling of the paired judgements made by examiners in the clinical examination (PACES) of MRCP(UK), where identical candidates were assessed in identical situations, allowing calculation of examiner stringency.MethodsData were analysed from the first nine diets of PACES, which were taken between June 2001 and March 2004 by 10,145 candidates. Each candidate was assessed by two examiners on each of seven separate tasks. with the candidates assessed by a total of 1,259 examiners, resulting in a total of 142,030 marks. Examiner demographics were described in terms of age, sex, ethnicity, and total number of candidates examined.ResultsFACETS suggested that about 87% of main effect variance was due to candidate differences, 1% due to station differences, and 12% due to differences between examiners in leniency-stringency. Multiple regression suggested that greater examiner stringency was associated with greater examiner experience and being from an ethnic minority. Male and female examiners showed no overall difference in stringency. Examination scores were adjusted for examiner stringency and it was shown that for the present pass mark, the outcome for 95.9% of candidates would be unchanged using adjusted marks, whereas 2.6% of candidates would have passed, even though they had failed on the basis of raw marks, and 1.5% of candidates would have failed, despite passing on the basis of raw marks.ConclusionExaminers do differ in their leniency or stringency, and the effect can be estimated using Rasch modelling. The reasons for differences are not clear, but there are some demographic correlates, and the effects appear to be reliable across time. Account can be taken of differences, either by adjusting marks or, perhaps more effectively and more justifiably, by pairing high and low stringency examiners, so that raw marks can be used in the determination of pass and fail.

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Firearm examination: Examiner judgments and computer-based comparisons.

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Firearm examination: Examiner judgments and computer-based comparisons.

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