The Factor of 10 in Forensic DNA Match Probabilities

• NCJ Number: 252188
• Author(s): Simone Gittelson, Tamvra R. Moretti, Anthony J. Onorato, Bruce Budowle, Bruce S. Weir, John Buckleton
• Date Published: May 2017
• Length: 10 pages
• Agencies: NIJ-Sponsored
• Award: Population Genetic Issues for Forensic DNA Profiles

Annotation

This article reports on an update that was performed on the classic experiments that led to the view that DNA profile probability assignments are usually within a factor of 10 of each other.

Abstract

The data used in this study consisted of 15 identifiler loci collected from a wide range of forensic populations. Following Budowle et al., the terms cognate and non-cognate were used. The cognate database was the database from which the profiles were simulated. The profile probability assignment was usually larger in the cognate database. In 44-65 percent of the cases, the profile probability for 15 loci in the non-cognate database was the database from which the profiles were simulated. The profile probability assignment was usually larger in the cognate database. In 44-65 percent of the cases, the profile probability for 15 loci in the non-cognate database was within a factor of 10 of the profile probability in the cognate database. This proportion was between 60 percent and 80 percent when the FBI and NIST data were used as the non-cognate databases. A second experiment compared the match probability assignment, using a generalized database and recommendation 4.2 from NRC II (the 4.2 assignment) with a proxy for the matching proportion developed using subpopulation allele frequencies and the product rule. The findings support that the 4.2 assignment has a large conservative bias. These results agree with previous research results. (Publisher abstract modified)