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Contains fulltext : 224762.pdf (publisher's version ) (Open Access), 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.

Radboud University, 22 juni 2021, Promotores : Witteman, C.L.M., Berger, C.E.H. Co-promotor : Stoel, R.D., Contains fulltext : 233894.pdf (Publisher’s version ) (Open Access), Forensic examiners provide answer to questions such as: "Is this bullet fired with this firearm?" or "Is this person the source of this fingerprint?". To provide an answer to these questions, the examiners evaluate the evidential material. Based on their observations, examiners provide a judgment about the source of the evidential material and how much support the evidence provides for this judgment (the evidential strength). The judgments of examiners are accepted in court on the merit of the examiners' training and experience. The court uses these judgments to decide about a person's innocence or guilt. To ensure that a suspect is not unjustly convicted or acquitted because of misrepresented forensic evidence, it is imperative that the reliability and validity of the examiners' judgments are known and as high possible, and that these judgments are unbiased. This dissertation shows that while the support for the reliability and validity of the examiners' source-judgments was quite high, they are not perfect. Examiners are not infallible and have difficulty providing calibrated evidential strength judgments. Furthermore, examiners are prone to bias by irrelevant information. Additional training, personal feedback, and support by the outcomes of computer-based methods could lead to better judgments. Adjusting standard operating procedures based on behavioral insights can minimize the occurrence of bias.

Contains fulltext : 218946.pdf (Publisher’s version ) (Closed access), Forensic firearm examiners compare the features in cartridge cases to provide a judgment addressing the question about their source: do they originate from one and the same or from two different firearms? In this article, the validity and reliability of these judgments is studied and compared to the outcomes of a computer-based method. The features we looked at were the striation patterns of the firing pin aperture shear marks of four hundred test shots from two hundred Glock pistols, which were compared by a computer-based method. Sixty of the resulting 79,800 comparisons were shown to 77 firearm examiners. They were asked to judge whether the cartridge cases had the same source or a different source, and to indicate the degree of support the evidence provided for those judgments. The results show that the true positive rates (sensitivity) and the true negative rates (specificity) of firearm examiners are quite high. The examiners seem to be slightly less proficient at identifying same-source comparisons correctly, while they outperform the used computer-based method at identifying different-source comparisons. The judged degrees of support by examiners who report likelihood ratios are not well-calibrated. The examiners are overconfident, giving judgments of evidential strength that are too high. The judgments of the examiners and the outcomes of the computer-based method are only moderately correlated. We suggest to implement performance feedback to reduce overconfidence, to improve the calibration of degree of support judgments, and to study the possibility of combining the judgments of examiners and the outcomes of computer-based methods to increase the overall validity.

Contains fulltext : 221387.pdf (Publisher’s version ) (Closed access), The rarity of general fingerprint patterns should be taken into account in the assessment of fingerprint evidence to provide a more complete assessment of fingerprint evidence than when only considering the minutiae. This should be done because, the rarer the corresponding pattern, the stronger the support for the hypothesis that the fingermark stems from the same source as the reference fingerprint. Fingerprint examiners' experience should enable them to provide meaningful assessments of the frequencies of these general patterns according to the theories of perceptual learning, exemplar theory of categorization and visual statistical learning. In this study we examined the accuracy of fingerprint examiners' and novices' judgments on the rarity of general fingerprint patterns. We found that fingerprint examiners seem to have acquired some knowledge about the rarity of general patterns, but had difficulty expressing this knowledge quantitatively using a novel sub-classification of general patterns. As a consequence, their judgments were not accurate and they did not perform better on this task than novices. For both participant groups judgments of more common patterns were more accurate. However, examiners did outperform novices in rank ordering general patterns from common to rare. We conclude that our study does not show that fingerprint examiners have expertise in explicitly judging frequencies of novel sub-classifications of general fingerprint patterns, but our results do indicate that the examiners have acquired knowledge about the rarity of patterns that novices do not possess.

Item does not contain fulltext, Objective: Forensic judgments and their peer review are often the result of human assessment and are thus subjective and prone to bias. This study examined whether bias affects forensic peer review. Hypotheses: We hypothesized that the probability of disagreement between two forensic examiners about the proposed conclusion would be higher with "blind" peer review (reviewer saw only the first examiner's comparison photos) than with "non-blind" peer review (reviewer also saw the first examiner's interpretation and proposed conclusion). We also hypothesized that examiners with a higher perceived professional status would have a larger effect on the reported conclusion than examiners with a lower status. Method: We acquired data during a non-blind and a blind peer review procedure in a naturalistic, covert study with eight examiners (3-26 years of experience). We acquired 97 conclusions of bullet and cartridge case comparisons in the blind and 471 in the non-blind peer review procedure. Results: The odds of disagreement between examiners about the evidential strength of a comparison were approximately five times larger (95%-CI [3.06, 8.50]) in the blind than in the non-blind procedure, with disagreement about 42.3% and 12.5% of the proposed conclusions, respectively. Also, the odds that their proposed conclusion was reported as the final conclusion were approximately 2.5 higher for the higher-status examiners than for lower-status examiners. Conclusions: Our results support both the hypothesis that bias occurs during non-blind forensic peer review and the hypothesis that higher-status examiners determine the outcome of a discussion more than lower-status examiners. We conclude that blind peer review may reduce the probability of bias and that status effects have an impact on the peer reviewing process.

The heritability of sensation seeking is investigated in an extended twin design, including mono- and dizygotic twins and their siblings. Besides a comparison of the phenotypic resemblance between monozygotic twins and dizygotic twins, the design allows for an explicit test of the assumption that results from twins may be generalized to the singleton population. Secondly, the design offers the opportunity to investigate to what extent the influence of common environment is the same for males and females and for twins and siblings, i.e. allowing for explicit tests of a special twin environment and of a sex-specific common environment. The results indicate that individual variation in sensation seeking is heritable, with few differences between males and females in heritability estimates for the sensation seeking dimensions. In contrast to prior studies, evidence is found for common environmental influences for thrill and adventure seeking in males, and experience seeking and boredom susceptibility in females. Evidence for a special twin environment was limited to boredom susceptibility in females. © 2006 Springer Science+Business Media, Inc.