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Database Extraction Strategies for Low-Template Evidence

NCJ Number
Forensic Science International: Genetics Volume: 9 Dated: March 2014 Pages: 134-141
Oyvind Bleka; Guro Dorum; Hinda Haned; Peter Gill
Date Published
March 2014
8 pages
This paper considers two types of search strategies in efforts to extract suspects from a DNA database, using methods based on probability arguments.
The authors introduce two probabilistic strategies for extracting a list of candidates from a DNA database. The term "probabilistic" means that the true donor is in the extracted list, given that he or she is in the database. One strategy is based on "the conditional method" used for familial search. The second strategy is inspired by "the profile centered method." It takes low-template data into consideration by conditioning on drop-out probabilities. The first strategy is limited by using the likelihood ratio (LR) match score, but the second strategy may use any of the match scores outlined in the paper. The performance of the proposed match scores is demonstrated by a study of each match score relative to the level of allele drop-out in the crime DNA sample, simulating low-template DNA. The efficiency was measured by random man simulation. The performance was compared using the SGM Plus kit and the ESX 17 kit for the Norwegian population. The ESX 17 kit demonstrated greater power in discovering perpetrators of crime in large national DNA databases. For future work, the database extraction procedure could be positioned into a Bayesian framework by specifying prior probabilities for the individuals in the database and calculating posterior odds of competing hypotheses. 3 tables, 3 figures, and 10 references