Rational bias in forensic science

An experimental study of blind proficiency tests in forensic science

“…In forensic science practice, moreover, crime-scene evidence is often ambiguous. The more ambiguous the evidence is, the harder it is to distinguish between deception and error (Whitman and Koppl (2009) help to explain why). Citing Schweitzer and Hsee (2002), Mazar and Ariely report, "participants are more likely to be dishonest as the private information they have becomes more ambiguous" (2006, p. 7).…”

“…As we have seen, the report says, "Forensic scientists who sit administratively in law enforcement agencies or prosecutors' offices, or who are hired by those units, are subject to a general risk of bias" (6-2). This statement may seem banal to some readers, but it contradicts the commonsense opinion of many forensic scientists (Whitman and Koppl 2009). Often, forensic scientists working in government crime labs genuinely believe that any forensic scientist working for defense counsel is venal, a "hired gun," and thus corrupt and untrustworthy.…”

“…In the context of forensic science, this message corresponds to a crime lab declaring, "match," "no match," or "inconclusive." (Whitman and Koppl (2009) defend this simplification.) The principal shape and the supplementary shape will sometimes be the same by chance.…”

“…This sequencing is more important the more ambiguous is the crime-scene evidence. Whitman and Koppl (2009) argue that sequential unmasking is necessary but not sufficient to ensure unbiased testing "because the very act of submitting a sample conveys information." Their model supports the view that blind proficiency tests would help to reduce errors in forensic science.…”

“…This fact very nearly follows from the fact that crime labs are typically organized under law enforcement agencies. Whitman and Koppl (2009) present a simple Bayesian model suggesting that the organization of forensic science may support a "rational" pro-prosecution bias. See Peart and Levy (2005) for a discussion of sympathy as a motive in economic theory.…”