The evidential strength of a combination of corresponding class features in tire examination.

Tire marks are an important type of forensic evidence as they are frequently encountered at crime scenes. When the tires of a suspect's car are compared, the evidence can be very strong if so-called 'acquired features' are observed to correspond. When only 'class characteristics' such as parts of the tire pattern are observed to correspond, it is obvious that many other tires will exist that also correspond, and so this evidence is usually considered very weak or is simply ignored. Like Benedict et al. (2014) we argue that such evidence can still be strong and should be taken into account. We describe a method for assessing the evidential strength of a set of corresponding class characteristics by presenting a case example from the Netherlands in which tire marks were obtained. Only part of two different tire patterns were visible, in combination with measurements on the axes width. Suitable databases were found already existing and accessible to forensic experts. We show how such data can be used to quantify the strength of evidence and how it can be reported. We also show how the risk of bias due to information surrounding the case may be minimized in cases like this. Our 'blind' procedure enables the expert to report a correspondence between class features in a more convincing way than standard procedures allow. In the particular exemplar case quite strong evidence was obtained, which was accepted and used by the Dutch court. We generalize this procedure for quantifying the evidential value of an expert's opinion of a correspondence. This examination procedure can be applied directly to other types of pattern evidence such as shoeprints, fingerprints, or images. Furthermore, it is 'blind' in the sense that the risk of contextual bias is minimized.

Paediatric femur fractures-the value of contextual information on judgement in possible child abuse cases: are we bias?

The majority of paediatric femur fractures result from accidental trauma; however, it is important to consider non-accidental trauma, especially in pre-ambulatory children. We study whether irrelevant contextual information subconsciously influences conclusions of healthcare professionals with respect to whether observations provide evidence for non-accidental trauma. A survey with nine radiographs of femur shaft fractures was designed. Two different clinical histories (vignettes) with contextual information were designed, non-abuse versus abuse context. One of both vignettes was randomly assigned to the radiograph shown to the participant, followed by a question with a 5-point answer scale, which represents a verbal expression of the likelihood ratio of the fracture regarding a non-accidental versus accidental cause. Participants were medical residents and staff members of different specialties from several Dutch hospitals. A total of 172 participants responded. The reported evidential strength of the vignettes with a non-abuse context was 0.19 (n = 784; 95%CI 0.10-0.28) and for the abuse context 0.94 (n = 764; 95%CI 0.86-1.02; p < 0.001). Women reported a stronger evidential strength than men, but both were influenced by context. Emergency department and paediatric doctors were more likely to decide that non-accidental trauma was the cause; paediatric radiologists were the least likely. Experience in years of practice and current function did not prevent participants from being bias.Conclusion: This study shows that the interpretation of medical results by healthcare professionals can be influenced by contextual information, such as low income and marital status, which are irrelevant to the decision as to whether abuse might have occurred. Given the same information about an injury, women, emergency department and paediatric doctors were more likely to decide that non-accidental trauma was the cause, while paediatric radiologists were least likely to decide this outcome. It is important to prevent contextual influence as much as possible, by recognizing it and implementing a management contextual information procedure. What is Known: • Contextual information is of possible influence on healthcare professionals in identifying non-accidental trauma. • Increased working experience is thought to be protective against this influence. What is New: • Contextual information influenced the interpretation of medical results by healthcare professionals regardless of work experience. • The interpretation of medical results by healthcare professionals is influenced by both affirmative and negative contextual information.

Firearm examination: Examiner judgments and computer-based comparisons.

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.

Cognitive biases in the peer review of bullet and cartridge case comparison casework: A field study.

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.

Assessing the frequency of general fingerprint patterns by fingerprint examiners and novices.

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.

Postmortem Computed Tomography in Firearm Homicides: A Retrospective Case Series.

Postmortem computed tomography (PMCT) is integrated into the evaluation of decedents in several American medical examiner offices and medicolegal death investigative centers in many other countries. We retrospectively investigated the value of PMCT in a series of firearm homicide cases from a statewide centralized medical examiner's office that occurred during 2016. Autopsies were performed or supervised by board-certified forensic pathologists who reviewed the PMCT scans prior to autopsy. PMCT scans were re-evaluated by a forensic radiologist blinded to the autopsy findings and scored by body region (head-neck, thoracoabdominal, and extremities). Injury discrepancies were scored using a modified Goldman classification and analyzed with McNemar's test. We included 60 males and 20 females (median age 31 years, range 3-73). Based on PMCT, 56 (79.1%) cases had injuries relevant to the cause of death in a single body region (24 head-neck region, 32 thoracoabdominal region). Out of these 56 cases, 9 had a missed major diagnosis by PMCT outside that region, including 6 extremity injuries visible during standard external examination. Yet all had evident lethal firearm injury. We showed that PMCT identifies major firearm injuries in homicide victims and excludes injuries related to the cause of death in other regions when a single body region is injured. Although PMCT has a known limited sensitivity for soft tissue and vascular pathology, it can be combined with external examination to potentially reduce or focus dissections in some of these cases depending on the circumstances and medicolegal needs.

Validity and reliability of forensic firearm examiners.

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.

Tracers as invisible evidence - The transfer and persistence of flock fibres during a car exchange.

This study assessed the recovery of flock fibres used as a tracer in a car exchange scenario. Flock fibres were deposited onto a car seat (or model thereof) and their transfer and persistence was investigated after a real or simulated car exchange. The overall aim of this study was to achieve an optimal use of flock fibres as tracers, i.e. to be able to select a fit-for-purpose flock fibre, to be able to predict the amount of flock fibres to be recovered from crime related items, and to be able to use these numbers to exclude accidental uptake. The effect of a number of variables on the transfer and persistence of flock fibres was studied, including flock fibre length, car upholstery, and trousers material. Laboratory based experiments were undertaken first, followed by realistic field based experiments. The flock fibres were captured in a non-destructive manner through fluorescence photography. A Matlab algorithm enabled fast automated counting of flock fibres on the images. Results indicate that an initial rapid loss of flock fibres from garments may be expected as a result of moderate movement. Although the amount of flock fibres to be recovered is affected by the flock fibre length, the type of car upholstery, and the type of trousers materials (if frictional force is taken into consideration), large numbers of flock fibres have been recovered from all target materials throughout the transfer route. These numbers are higher than the amount of flock fibres recovered due to accidental uptake. In conclusion, flock fibres can serve as invisible evidence to reconstruct a series of events.

Ricochet Behavior on Glass-Critical Ricochet Angles, Ricochet Angles, and Deflection Angles.

For shooting scene reconstruction purposes, knowledge about the ricochet behavior of bullets provides valuable information. In this study, the critical ricochet angles of four cartridge types were established on plain float glass. The estimates of the critical ricochet angles varied between cartridge types and were 21.0° for .32 Auto FMJ bullets, 15.8° for 9 mm Luger FMJ bullets, 17.6° for .45 Auto FMJ bullets, and 21.3° for 9 mm Luger, Action NP bullets. The corresponding ricochet and deflection angles per incidence angle varied depending on the state of the ricocheted bullets. The mean ricochet angles are always lower than the corresponding angles of incidence, and the mean ricochet angles for the FMJ bullets with undamaged jackets are lower than those of bullets where the jacket is either damaged or the bullet partially ricocheted and partially perforated. Mean ricochet angles are lower for undamaged FMJ bullets than for undamaged Action NP bullets.

Effects of CBRN decontaminants in common use by first responders on the recovery of latent fingerprints--assessment of the loss of ridge detail on glass.

Following a CBRN incident, first responders use decontamination procedures to reduce the risk of exposure. The effect of decontamination on forensic trace material has, however, not been fully examined. This study sought to evaluate the effect of five different physical or chemical decontamination materials on the recovery of latent fingerprints. Fingerprints were deposited on glass slides, decontaminated, and assessed on the presence of ridge detail. The results demonstrate that decontamination affects the quality of latent fingerprints substantially. On at least 61% of the fingerprints, a reduced amount of ridge detail was observed upon decontamination. Furthermore, development with cyanoacrylate appeared not to succeed anymore. Instead, the ability of vacuum metal deposition to successfully develop decontaminated fingerprints is demonstrated. The results from this study may contribute to an increased forensic awareness regarding decontamination and emphasize the necessity for further research into new item decontamination procedures or new forensic initiatives prior to decontamination.

Opening the psychological black box in genetic counseling. The psychological impact of DNA testing is predicted by the counselees' perception, the medical impact by the pathogenic or uninformative BRCA1/2-result.

BACKGROUND: It has been hypothesized that the Outcomes of DNA testing (O) are better predicted and/or mediated by the counselees' Perception P) than by the actually communicated genetic Information (I). In this study, we aimed at quantifying the effect that perception has in genetic counseling for hereditary breast/ovarian cancer. METHODS: Two hundred and four women, who had previously been tested for BRCA1/2, participated in a retrospective questionnaire study; 93% had cancer. Communicated Information (I) consisted of cancer risks and BRCA1/2 test result category: unclassified variant (n = 76), uninformative (n = 76), pathogenic mutation (n = 51). Four perception variables (P) were included: the counselees' recollections and interpretations of both the cancer risks and the likelihood that the cancer in their family is heritable. The Outcome variables (O) included life changes, counselees' medical decisions, BRCA-related self-concept, current psychological well-being, and quality-of-life. Bootstrap mediation analyses determined whether relationships were direct (I→O or P→O) or indirect through the mediation of perception (I→P→O). RESULTS: The actually communicated pathogenic mutation and uninformative result directly predicted medical decisions (I→O), i.e. intended and performed surgery of breasts/ovaries. All other outcomes were only directly predicted by the counselees' perception (recollection and interpretation) of their cancer risks and heredity likelihood (P→O), or this perception mediated the outcome (I→P→O). However, this perception was significantly different from the actually communicated cancer risks (I→P). Unclassified variants were inaccurately perceived (mostly overestimated); this misperception predicted both psychological outcomes and radical medical decisions. DISCUSSION: Genetic counselors need to explicitly address the counselee's interpretations and intended medical decisions. In case of misinterpretations, additional counseling might be offered. Communication of unclassified variants needs special attention given the pitfall of overestimation of risk.

Improving the point of origin determination in bloodstain pattern analysis.

In bloodstain pattern analysis, it is important to know the point of origin (PO) of an impact pattern. This point can be estimated by means of the stringing method, the tangent method, or by commercially available computer programs. In this study, the accuracy of two computer programs was investigated under different conditions. Impact patterns were created by means of a modified mouse trap, and subsequently the PO was calculated. By examining the characteristics of single bloodstains, the influence on the deviation could be determined. To improve the estimation of the PO, it is important to select bloodstains that lie close to the presumable location of the blood source, that are large (width >1.5 mm) and that show an elliptical form. If possible, bloodstains from different walls should be taken into account. Our recommendations may improve the PO determination of impact patterns.

Correction to Tzidony and Ravreby (1992): a statistical approach to drug sampling: a case study.

In 1992, Tzidony and Ravreby presented a confidence interval for the total weight of a seizure of illicit drugs present in a population. Their approach has subsequently been applied by several researchers in the field. The formula on which their approach is based does, however, not fully take into account the proportion of drug units found in the sample. In this paper, a modification is presented that consistently uses the correct sample size in all terms of the confidence interval, based on the proportion of drug units found in the sample. The effective sample size is smaller than the original sample size, and this should consequently be accounted for in the estimation of the standard error and in the corresponding t-distribution. The new confidence interval is again based on the assumption that the proportion of drug units in the population is known after sampling.

Comparison of frequentist methods for estimating the total weight of consignments of drugs.

A topic in forensic statistics is the estimation of the total weight of consignments of drugs based on subsamples of which a certain fraction may not contain drugs at all. The frequentist approach to this concentrates on obtaining confidence intervals for the total weight, based on estimation of the fraction of drugs and the mean and variance of the weights of drug units. The current study shows that the resulting confidence intervals are basically unreliable, since they are based on an underestimation of the variation of the underlying statistical process. Two alternatives are given that yield asymptotically correct results. These are not reliable for small subsamples either, though, because of the inherent multimodal behaviour of the sample mean. In cases where a relatively large fraction of the consignment contains no drugs, the confidence intervals reported in the literature should not be used in practice.

On the likelihood ratio test in structural equation modeling when parameters are subject to boundary constraints.

The authors show how the use of inequality constraints on parameters in structural equation models may affect the distribution of the likelihood ratio test. Inequality constraints are implicitly used in the testing of commonly applied structural equation models, such as the common factor model, the autoregressive model, and the latent growth curve model, although this is not commonly acknowledged. Such constraints are the result of the null hypothesis in which the parameter value or values are placed on the boundary of the parameter space. For instance, this occurs in testing whether the variance of a growth parameter is significantly different from 0. It is shown that in these cases, the asymptotic distribution of the chi-square difference cannot be treated as that of a central chi-square-distributed random variable with degrees of freedom equal to the number of constraints. The correct distribution for testing 1 or a few parameters at a time is inferred for the 3 structural equation models mentioned above. Subsequently, the authors describe and illustrate the steps that one should take to obtain this distribution. An important message is that using the correct distribution may lead to appreciably greater statistical power.