Rational Bias in Forensic Science

Posted: 22 Mar 2010

See all articles by Douglas Glen Whitman

Douglas Glen Whitman

California State University, Northridge - Department of Economics

Roger Koppl

Whitman School of Management


The current organization of forensic science induces biases in the conduct of forensic science even if forensic scientists are perfectly rational. Assuming forensic examiners are flawless Bayesian statisticians helps us to identify structural sources of error that we might otherwise have undervalued or missed altogether. Specifically, forensic examiners’ conclusions are affected not just by objective test results but also by two subjective factors: their prior beliefs about a suspect's likely guilt or innocence and the relative importance they attach to convicting the guilty rather than the innocent. The authorities-police and prosecutors-implicitly convey information to forensic examiners by their very decision to submit samples for testing. This information induces the examiners to update their prior beliefs in a manner that results in a greater tendency to provide testimony that incriminates the defendant. Forensic results are in a sense ‘contaminated’ by the prosecution and thus do not provide jurors with an independent source of information. Structural reforms to address such problems of rational bias include independence from law enforcement, blind proficiency testing and separation of test from interpretation.

Keywords: forensic science, bias, Bayesian, NAS report, organization

Suggested Citation

Whitman, Douglas Glen and Koppl, Roger, Rational Bias in Forensic Science. Law, Probability & Risk, Vol. 9, No. 1, pp. 69-90, 2010, Available at SSRN: https://ssrn.com/abstract=1575956 or http://dx.doi.org/10.1093/lpr/mgp028

Douglas Glen Whitman (Contact Author)

California State University, Northridge - Department of Economics ( email )

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United States
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Roger Koppl

Whitman School of Management ( email )

United States
(315) 443-4543 (Phone)
(315) 442-1449 (Fax)

HOME PAGE: http://whitman.syr.edu/faculty-and-research/faculty/showInfo.aspx?id=468

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