Enhancing the Potential of Very Partial DNA Database Matches for Investigation Using Dynamic Cutoff Lr Thresholds – a Proof of Concept

Abstract

The concept of using a minimum number of short tandem repeat loci in national and international DNA database searches has long been employed to establish reliable matches. However, this approach may unintentionally overlook matches with valuable intelligence potential, especially when the minimum loci requirement is not met. In this study, we propose a paradigm shift by introducing a dynamic likelihood ratio threshold as an additional criterion for reporting DNA matches that fall short of the minimum number of loci but possess a sufficient likelihood ratio, thereby providing valuable intelligence leads. We discuss the theoretical basis behind this approach, its potential benefits including the proportion of true-positive matches which may be saved from an automatic rejection, and provide advice on the implementation of the method depending on the level of stringency required and the size of the national DNA database.

Keywords: DNA Database, partial matches, likelihood ratio, dynamic cutoff threshold