Duke University

presents:

Bruce S. Weir

North Carolina State University

"Statistical Issues in Interpreting DNA Profile Matches"

Abstract:

When a match is found between DNA profiles in an evidentiary stain and a blood sample from a suspect, it is usual to supply some number expressing the strength of this evidence. Simply quoting the frequency of the matching profile in some population is not satisfactory, and can be misleading. It is better to provide a likelihood ratio, formed as the probability of the profile under the prosecution explanation divided by the probability of the profile under the defense explanation. These likelihood ratios depend on population genetic principles, and do not incorporate non-quantifiable effects that might be caused by fraud or incompetence.

Likelihood ratios are especially necessary when an evidentiary stain contains the DNA profile of more than one contributor. The evidence can be substantially over- or under-stated if only the frequencies with which unknown contributors have the stain profile are presented in court.

Although statistics has played a role in interpreting DNA profile matches, the highly discriminatory nature of the profiles now being determined suggsts that this need may have passed.

Friday, January 19, 1996

11:45 - 12:45

130 Sociology/Psychology Building

Any questions concerning the seminar may be addressed to Cheryl McGhee @[919] 684-8029, e-mail cheryl@stat.duke.edu, or finger seminar@stat.duke.edu