Koehler, J. J. (1993). Error and Exaggeration in the Presentation of DNA Evidence. Jurimetrics Journal. 34, 21-39.

ABSTRACT

This paper 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 inferential chain in Figure 1: (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? Section II addresses the first question and includes discussion on ways of defining and estimating the false positive error rates at DNA laboratories.

Sections III and IV address the second and third questions respectively. These sections introduce the Source Probability and Ultimate Issue Errors and show how these errors are often committed by experts at trial with assistance from attorneys on both sides. Section V introduces two related exaggerations, the P (Another Match) error and the Numerical Conversion Error. Section VI provides a simple and general explanation for the persistence of the identified errors. Section VII 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.