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An Investigation into Compound Likelihood Ratios for Forensic DNA Mixtures

NCJ Number
307020
Journal
Genes Volume: 14 Issue: 3 Dated: March 2023 Pages: 714
Author(s)
Richard Wivell; Hannah Kelly; Jason Kokoszka; Jace Daniels; Laura Dickson; John Buckleton; Jo-Anne Bright
Date Published
March 2023
Annotation

This article presents research into utilizing compound likelihood ratios when analyzing forensic DNA mixtures.

Abstract

Simple propositions are defined as those with one POI and the remaining contributors unknown under Hp and all unknown contributors under Ha. Conditional propositions are defined as those with one POI, one or more assumed contributors, and the remaining contributors (if any) unknown under Hp, and the assumed contributor(s) and N unknown contributors under Ha. In this study, compound propositions are those with multiple POI and the remaining contributors unknown under Hp and all unknown contributors under Ha. The authors study the performance of these three proposition sets on thirty-two samples (two laboratories × four NOCs × four mixtures) consisting of four mixtures, each with N = 2, N = 3, N = 4, and N = 5 contributors using the probabilistic genotyping software, STRmix™. In this study, it was found that conditional propositions have a much higher ability to differentiate true from false donors than simple propositions. Compound propositions can misstate the weight of evidence given the propositions strongly in either direction. (Published Abstract Provided)