As illustrated by the mistaken, high-profile fingerprint identification of Brandon Mayfield in the Madrid Bomber case, and consistent with a recent critique by the National Academy of Sciences (2009), it is clear that the forensic sciences are subject to contextual bias and fraught with error. In this article, we describe classic psychological research on primacy, expectancy effects, and observer effects, all of which indicate that context can taint people's perceptions, judgments, and behaviors. Then we describe recent studies indicating that confessions and other types of information can set into motion forensic confirmation biases that corrupt lay witness perceptions and memories as well as the judgments of experts in various domains of forensic science. Finally, we propose best practices that would reduce bias in the forensic laboratory as well as its influence in the courts.

Exposure to irrelevant contextual information prompts confirmation-biased judgments of forensic science evidence . Nevertheless, some forensic examiners appear to believe that blind testing is unnecessary. To assess forensic examiners' beliefs about the scope and nature of cognitive bias, we surveyed 403 experienced examiners from 21 countries. Overall, examiners regarded their judgments as nearly infallible and showed only a limited understanding and appreciation of cognitive bias. Most examiners believed they are immune to bias or can reduce bias through mere willpower, and fewer than half supported blind testing. Furthermore, many examiners showed a bias blind spot (Pronin, Lin, & Ross, 2002), acknowledging bias in other domains but not their own, and in other examiners but not themselves. These findings underscore the necessity of procedural reforms that blind forensic examiners to potentially biasing information, as is commonplace in other branches of science.

The biases that may have led to unjustified deaths by police actions have received much attention and have been extensively discussed (e.g., [1][2][3]), but are the deceased also subject to bias after their death by scientists examining their bodies? Are scientists biased by race or other irrelevant contextual information [4]?Forensic pathologists play a critical part in administering justice because of their role in criminal investigations and court proceedings, as they determine whether the manner of death was homicide vs. something else (e.g., accidental or suicide).Despite bias plaguing many forensic domains [5], forensic scientists often deny that bias can impact their decisions (the bias blind spot [6], and the fallacies of expert immunity and illusion of control [7]).Especially acute has been the resistance to adopt policies that minimize bias, which has "been met with stern resistance from the forensic pathology community" ([8] p. 261). However, cognitive bias

Decision-making of mental health professionals is influenced by irrelevant information (e.g., Murrie, Boccaccini, Guarnera, & Rufino, 2013). However, the extent to which mental health evaluators acknowledge the existence of bias, recognize it, and understand the need to guard against it, is unknown. To formally assess beliefs about the scope and nature of cognitive bias, we surveyed 1,099 mental health professionals who conduct forensic evaluations for the courts or other tribunals (and compared these results with a companion survey of 403 forensic examiners, reported in Kukucka, Kassin, Zapf, & Dror, 2017). Most evaluators expressed concern over cognitive bias but held an incorrect view that mere willpower can reduce bias. Evidence was also found for a bias blind spot (Pronin, Lin, & Ross, 2002), with more evaluators acknowledging bias in their peers’ judgments than in their own. Evaluators who had received training about bias were more likely to acknowledge cognitive bias as a cause for concern, whereas evaluators with more experience were less likely to acknowledge cognitive bias as a cause for concern in forensic evaluation as well as in their own judgments. Training efforts should highlight the bias blind spot and the fallibility of introspection or conscious effort as a means of reducing bias. In addition, policies and procedural guidance should be developed in regard to best cognitive practices in forensic evaluations.

Citing classic psychological research and a smattering of recent studies, Kassin, Dror, and Kukucka (2013) proposed the operation of a forensic confirmation bias, whereby preexisting expectations guide the evaluation of forensic evidence in a self-verifying manner. In a series of studies, we tested the hypothesis that knowing that a defendant had confessed would taint people's evaluations of handwriting evidence relative to those not so informed. In Study 1, participants who read a case summary in which the defendant had previously confessed were more likely to erroneously conclude that handwriting samples from the defendant and perpetrator were authored by the same person, and were more likely to judge the defendant guilty, compared with those in a no-confession control group. Study 2 replicated and extended these findings using a within-subjects design in which participants rated the same samples both before and after reading a case summary. These findings underscore recent critiques of the forensic sciences as subject to bias, and suggest the value of insulating forensic examiners from contextual information.