Activity-level evaluation of DNA transfer to stockings: comparisonof HaloGen with simplified contributor-based approaches
DNA findings on clothing are often evaluated at sub-source level to address whether a person contributed DNA to a sample. In many cases, however, the disputed issue is not whose DNA is present, but how the DNA was transferred. This paper applies the HaloGen framework to evaluate DNA findings on stockings under activity-level propositions. The data derive from controlled experiments, reported in a…
This study compares the HaloGen framework to simplified contributor-based approaches when evaluating DNA transfer to stockings. The focus is on understanding how DNA is transferred, rather than identifying who contributed it. Controlled experiments were conducted, comparing active contact (a person of interest pulling down stockings) with social contact (the person of interest and wearer using the same bathroom).
DNA quantities from two stained stockings were analyzed, with the Pop20 reference range used as a prior for Bayesian modeling. The study utilized data from 20 laboratories to update the model, and prior-sensitivity and leave-one-case-out analyses showed that the results were robust to prior choice. HaloGen was shown to perform better than simplified approaches, which reduce DNA quantities to binary or categorical states.
These simplified methods may lead to loss of information and affect likelihood ratios. The study highlights the importance of preserving contributor-level symmetry, as an observed unknown contributor should not be automatically downgraded to background unless it represents an alternative direct actor.
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