Choice of population database for forensic DNA profile analysis

Autor: Christopher D, Steele, David J, Balding
Rok vydání: 2014
Předmět:
Zdroj: Science & Justice
ISSN: 1355-0306
Popis: When evaluating the weight of evidence (WoE) for an individual to be a contributor to a DNA sample, an allele frequency database is required. The allele frequencies are needed to inform about genotype probabilities for unknown contributors of DNA to the sample. Typically databases are available from several populations, and a common practice is to evaluate the WoE using each available database for each unknown contributor. Often the most conservative WoE (most favourable to the defence) is the one reported to the court. However the number of human populations that could be considered is essentially unlimited and the number of contributors to a sample can be large, making it impractical to perform every possible WoE calculation, particularly for complex crime scene profiles. We propose instead the use of only the database that best matches the ancestry of the queried contributor, together with a substantial FST adjustment. To investigate the degree of conservativeness of this approach, we performed extensive simulations of one- and two-contributor crime scene profiles, in the latter case with, and without, the profile of the second contributor available for the analysis. The genotypes were simulated using five population databases, which were also available for the analysis, and evaluations of WoE using our heuristic rule were compared with several alternative calculations using different databases. Using FST = 0.03, we found that our heuristic gave WoE more favourable to the defence than alternative calculations in well over 99% of the comparisons we considered; on average the difference in WoE was just under 0.2 bans (orders of magnitude) per locus. The degree of conservativeness of the heuristic rule can be adjusted through the FST value. We propose the use of this heuristic for DNA profile WoE calculations, due to its ease of implementation, and efficient use of the evidence while allowing a flexible degree of conservativeness.
Highlights • A heuristic rule of assuming the database of Q for all unprofiled individuals in a CSP is proposed. • We simulate a total of 105 000 one- and two-contributor CSPs with no dropin or dropout. • The heuristic rule is conservative compared to an alternative for the majority of simulated CSPs. • We suggest that the use of this heuristic will allow for evaluation of complex cases with many possible databases.
Databáze: OpenAIRE
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