Testing Likelihood Ratios Produced From Complex DNA Profiles

• NCJ Number: 249335
• Author(s): Duncan Taylor, John Buckleton
• Date Published: March 2015
• Length: 7 pages
• Agencies: NIJ-Sponsored
• Award: Population Genetic Issues for Forensic DNA Profiles

Annotation

This study investigated a number of diagnostics in assessing the performance of a model (Hd true tests) for testing likelihood ratios produced from complex DNA profiles.

Abstract

The performance of any model used to analyze DNA profile evidence should be tested using simulation, large-scale validation studies based on ground-truth cases, or alignment with trends predicted by theory. The focus of the current work was the proportion of comparisons to non-contributors that yield a likelihood ratio (LR) higher than or equal to the likelihood ratio of a known contributor (LRPOI), designated as p, and the average LR for Hd true tests. Theory predicts that p should always be less than or equal to 1/LRPOI and hence the observation of this in any particular case is of limited use. A better diagnostic is the average LR for Hd true which should be near to 1. The current study tested the performance of a continuous interpretation model on nine DNA profiles of varying quality and complexity and verified the theoretical expectations. (Publisher abstract modified)