Error and Exaggeration in the Presentation of DNA Evidence at Trial

Jurimetrics Journal, Vol. 34, p. 21, 1993

20 Pages Posted: 12 Jul 2009 Last revised: 17 May 2014

Date Written: 1993

Abstract

This Article identifies some of the subtle, but common, exaggerations that have occurred at trial, and classifies each in relation to the three questions that are suggested by the chain of reasoning sketched above: (1) Is a reported match a true match? (2) Is the suspect the source of the trace? (3) Is the suspect the perpetrator of the crime? Part I addresses the first question and discusses ways of defining and estimating the false positive error rates at DNA laboratories. Parts II and III address the second and third questions, respectively. These sections introduce the "source probability error" and "ultimate issue error" and show how experts often commit these errors at trial with assistance from attorneys on both sides. Part IV introduces two related exaggerations, the "P(Another Match) error" and the "numerical conversion error." Part V provides a simple and general explanation for the persistence the errors identified. Part VI concludes with a discussion of the ways in which scientists can take advantage of their roles as teachers, expert witnesses, and researchers to educate the courts about the meaning and limits of probabilistic DNA evidence.

Keywords: DNA, match statistics, error

Suggested Citation

Koehler, Jonathan J., Error and Exaggeration in the Presentation of DNA Evidence at Trial (1993). Jurimetrics Journal, Vol. 34, p. 21, 1993. Available at SSRN: https://ssrn.com/abstract=1432065

Jonathan J. Koehler (Contact Author)

Northwestern University - Pritzker School of Law ( email )

375 E. Chicago Ave
Chicago, IL 60611
United States

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