Are forensic scientists too risk averse?

Unpacking workplace stress and forensic expert decision-making: From theory to practice

Workplace stress can affect forensic experts' job satisfaction and performance, which holds financial and other implications for forensic service providers. Therefore, it is important to understand and manage workplace stress, but that is not simple or straightforward. This paper explores stress as a human factor that influences forensic expert decision-making. First, we identify and highlight three factors that mitigate decisions under stress conditions: nature of decision, individual differences, and context of decision. Second, we situate workplace stress in forensic science within the Challenge-Hindrance Stressor Framework. We argue that stressors in forensic science workplaces can have a positive or a negative impact, depending on the type, level, and context of stress. Developing an understanding of the stressors, their sources, and their possible impact can help forensic service providers and researchers to implement context-specific interventions to manage stress at work and optimize expert performance.

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

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

Tracking the growth of visual evidence in fingerprint comparison tasks

Fingerprint comparisons are extended in time due to the fine details (minutiae) that necessitate multiple eye fixations throughout the comparison. How is evidence accumulated across these multiple regions? The present work measures decisions at multiple points during a comparison to address how feature diagnosticity and image clarity play a role in evidence accumulation. We find that evidence is accumulated at a constant rate over time, with evidence for identification and exclusion accumulated at similar rates. Manipulations of image diagnosticity and image clarity demonstrate two exceptions to this constant rate: Highly diagnostic evidence followed by weak evidence tends to lose the initial benefits of the strong start, and low image clarity at the start of the comparison can be overcome with high image clarity at the end of the comparison. The results suggest that examiners tend to treat each region fairly independently (as demonstrated by linear evidence accumulation), with only weak evidence for hysteresis effects that tend to fade as additional regions are presented. Data from transition probability matrices support an incremental evidence accumulation account, with very little evidence for rapid "aha" moments even for exclusion decisions. The results are consistent with a model in which each fixated region contributes an independent unit of evidence, and these accumulate to form an eventual decision. Fingerprint comparisons do not seem to depend on which regions are selected first, and thus examiners need not worry about finding the most diagnostic region first, but instead focus on conducting a complete analysis of the latent print.

Statistical feature training improves fingerprint-matching accuracy in novices and professional fingerprint examiners

Forensic science practitioners compare visual evidence samples (e.g. fingerprints) and decide if they originate from the same person or different people (i.e. fingerprint ‘matching’). These tasks are perceptually and cognitively complex—even practising professionals can make errors—and what limited research exists suggests that existing professional training is ineffective. This paper presents three experiments that demonstrate the benefit of perceptual training derived from mathematical theories that suggest statistically rare features have diagnostic utility in visual comparison tasks. Across three studies (N = 551), we demonstrate that a brief module training participants to focus on statistically rare fingerprint features improves fingerprint-matching performance in both novices and experienced fingerprint examiners. These results have applied importance for improving the professional performance of practising fingerprint examiners, and even other domains where this technique may also be helpful (e.g. radiology or banknote security).

The low prevalence effect in fingerprint comparison amongst forensic science trainees and novices

The low prevalence effect is a phenomenon whereby target prevalence affects performance in visual search (e.g., baggage screening) and comparison (e.g., fingerprint examination) tasks, such that people more often fail to detect infrequent target stimuli. For example, when exposed to higher base-rates of 'matching' (i.e., from the same person) than 'non-matching' (i.e., from different people) fingerprint pairs, people more often misjudge 'non-matching' pairs as 'matches'-an error that can falsely implicate an innocent person for a crime they did not commit. In this paper, we investigated whether forensic science training may mitigate the low prevalence effect in fingerprint comparison. Forensic science trainees (n = 111) and untrained novices (n = 114) judged 100 fingerprint pairs as 'matches' or 'non-matches' where the matching pair occurrence was either high (90%) or equal (50%). Some participants were also asked to use a novel feature-comparison strategy as a potential attenuation technique for the low prevalence effect. Regardless of strategy, both trainees and novices were susceptible to the effect, such that they more often misjudged non-matching pairs as matches when non-matches were rare. These results support the robust nature of the low prevalence effect in visual comparison and have important applied implications for forensic decision-making in the criminal justice system.

Validating strength-of-support conclusion scales for fingerprint, footwear, and toolmark impressions

In the pattern comparison disciplines such as fingerprints, footwear, and toolmarks, the results of a comparison are communicated by examiners in the form of categorical conclusions such as Identification or Exclusion. These statements have been criticized as requiring knowledge of prior probabilities by the examiners and being overinterpreted by laypersons. Alternative statements based on strength-of-support language have been proposed. The current study compares traditional conclusion scales against strength-of-support scales to determine how these new statements might be used by examiners in casework. Each participant completed 60 comparisons within their discipline, which were designed to approximate casework conditions, using either a traditional or a strength-of-support conclusion scale. The scale used on each trial was randomly assigned, and participants knew the scale for that trial as they began the comparison. Fingerprint examiners were much less likely to use Extremely Strong Support for Common Source than Identification. Footwear examiners treated the traditional and strength-of-support scales similarly, but toolmark examiners were much less likely to use Extremely Strong Support for Common Source than Identification, similar to fingerprint examiners. A separate group of fingerprint examiners used Identification less often when an expanded scale was available. The results demonstrate that expanded scales may result in the highest conclusion category being used less often by examiners when other alternatives are possible, and the term "extremely strong support" may introduce risk aversion on the part of examiners.

Challenges to reasoning in forensic science decisions

The success of forensic science depends heavily on human reasoning abilities. Although we typically navigate our lives well using those abilities, decades of psychological science research shows that human reasoning is not always rational. In addition, forensic science often demands that its practitioners reason in non-natural ways. This article addresses how characteristics of human reasoning (either specific to an individual or in general) and characteristics of situations (either specific to a case or in general in a lab) can contribute to errors before, during, or after forensic analyses. In feature comparison judgments, such as fingerprints or firearms, a main challenge is to avoid biases from extraneous knowledge or arising from the comparison method itself. In causal and process judgments, for example fire scenes or pathology, a main challenge is to keep multiple potential hypotheses open as the investigation continues. Considering the contributions to forensic science judgments by persons, situations, and their interaction, reveals ways to develop procedures to decrease errors and improve accuracy.

Stressors in forensic organizations: Risks and solutions

Stressors of many types occur in forensic laboratories, with detrimental effects for individuals, laboratory systems, and casework outcomes. These stressors may be general, affecting the entire laboratory or all cases, or specific, affecting individual examiners or single cases. Stressors affecting individual examiners include: vicarious trauma associated with details of worked cases, nonstandard working hours, fatigue, the monotony of repetitious tasks, fear of errors, and severe backlogs. Policies and laboratory cultures can be put in place to minimize the effects of stressors; however, current forensic organizational responses to these stressors may vary from punitive to collaborative approaches. This article presents several models and case studies that can help inform the creation of positive laboratory policies. A system of discipline-wide centralized error reporting, similar to systems used to reduce fatal mistakes in medicine and aviation, could have the potential to identify areas of concern within forensic science practices.