Interpreting Forensic DNA Profiling evidence without specifying the number of contributors

• NCJ Number: 249330
• Author(s): Duncan Taylor, Jo-Anne Bright, John Buckleton
• Date Published: November 2014
• Length: 12 pages
• Agencies: NIJ-Sponsored
• Award: Population Genetic Issues for Forensic DNA Profiles

Annotation

This article reports on the demonstration of an MCMC method of correctly weighting analyses of DNA profile data that spans a range of contributors, and it explores the theoretical behavior of such a weight and applies these theories using practical examples; also discussed are issues in omitting this weight term from the LR calculation when considering different numbers of contributors in the one calculation.

Abstract

DNA profile interpretation has benefited from recent improvements that use semi-continuous or fully continuous methods to interpret information within an electropherogram. These methods are likelihood-ratio-based and currently require that a number of contributors be assigned prior to analysis. Often there is ambiguity in the choice of number of contributors, and an analyst is left with the task of determining what they believe to be the most probable number. The choice can be particularly important when the difference between two possible contributor numbers means the difference between excluding a person of interest as being a possible contributor, and producing a statistic that favors their inclusion. Presenting both options in a court of law places the decision with the court. (Publisher abstract modified)