NCJ Number
229589
Journal
Forensic Science International: Genetics Volume: 4 Issue: 1 Dated: December 2009 Pages: 1-10
Date Published
December 2009
Length
10 pages
Annotation
This article examines an approach developed for the analysis and interpretation of low template DNA (LTDNA) profiles.
Abstract
This article discusses the interpretation of DNA profiles obtained from low template DNA samples. The most important challenge to interpretation in this setting arises when either or both of "drop-out" and "drop-in" create discordances between the crime scene DNA profile and the DNA profile expected under the prosecution allegation. Stutter and unbalanced peak heights are also problematic, in addition to the effects of masking from the profile of a known contributor. The article outlines a framework for assessing such evidence, based on likelihood ratios that involve drop-out and drop-in probabilities, and apply it to two casework examples. The framework extends previous work , including a new approaches to modeling homozygote drop-out and uncertainty in allel calls for stutter, masking, and near-threshold peaks. It shows that some current approaches to interpretation, such as ignoring a discrepant locus or reporting a "Random Man Not Excluded" (RMNE) probability can be systematically unfair to defendants. It also shows that the likelihood ratio (LR) can depend strongly on the assumed value for the drop-out probability, and there is typically no approximation that is useful for all values. The article illustrates that ignoring the possibility of drop-in is usually unfair to defendants, and argues that under circumstances in which the prosecution relies on drop-out, it might be unsatisfactory to ignore any possibility of drop-in. Figures, tables, and references (Published Abstract)