Statistical Evaluation of Forensic DNA Profile Evidence

The evaluation of weight of evidence for forensic DNA profiles has been a subject of controversy since their introduction over 20 years ago. Substantial progress has been made for standard DNA profiles, but new issues have arisen in recent years with the advent of more sensitive profiling techniques, allowing profiles to be recovered from minuscule amounts of possibly degraded DNA. These low-template DNA profiles suffer from enhanced stochastic effects, including dropin, dropout, and stutter, which pose problems for DNA profile evaluation. These problems are now beginning to be overcome with the emergence of several statistical models and software. We first review the general principles of statistical evaluation of DNA profile evidence, and we then focus on low-template DNA profiles, briefly reviewing the main statistical models and software. We cover methods that use allele presence/absence and those that use electropherogram peak heights, focusing on the likelihood ratio as measure of evidential weight.