title: Searching mixed DNA profiles directly against profile databases.
abstract: DNA databases have revolutionised forensic science. They are a powerful investigative tool as they have the potential to identify persons of interest in criminal investigations. Routinely, a DNA profile generated from a crime sample could only be searched for in a database of individuals if the stain was from single contributor (single source) or if a contributor could unambiguously be determined from a mixed DNA profile. This meant that a significant number of samples were unsuitable for database searching. The advent of continuous methods for the interpretation of DNA profiles offers an advanced way to draw inferential power from the considerable investment made in DNA databases. Using these methods, each profile on the database may be considered a possible contributor to a mixture and a likelihood ratio (LR) can be formed. Those profiles which produce a sufficiently large LR can serve as an investigative lead. In this paper empirical studies are described to determine what constitutes a large LR. We investigate the effect on a database search of complex mixed DNA profiles with contributors in equal proportions with dropout as a consideration, and also the effect of an incorrect assignment of the number of contributors to a profile. In addition, we give, as a demonstration of the method, the results using two crime samples that were previously unsuitable for database comparison. We show that effective management of the selection of samples for searching and the interpretation of the output can be highly informative.
authors: Institute of Environmental Science and Research Limited, Private Bag 92021, Auckland 1142, New Zealand; Department of Statistics, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. Electronic address: Jo.bright@esr.cri.nz.
authors: Jo-Anne
authors: JA
authors: Bright
authors: Forensic Science South Australia, 21 Divett Place, Adelaide, SA 5000, Australia.
authors: Duncan
authors: D
authors: Taylor
authors: Department of Statistics, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
authors: James
authors: J
authors: Curran
authors: Institute of Environmental Science and Research Limited, Private Bag 92021, Auckland 1142, New Zealand.
authors: John
authors: J
authors: Buckleton
mesh_terms: D004247:DNA / Q000235:genetics*; D016172:DNA Fingerprinting; D030561:Databases, Nucleic Acid; D005838:Genotype; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D012661:Semen / Q000737:chemistry
chemical_list: D004247:DNA
keywords: Continuous models; Database; Forensic DNA; Likelihood ratio