title: Helping to distinguish primary from secondary transfer events for trace DNA.
abstract: DNA is routinely recovered in criminal investigations. The sensitivity of laboratory equipment and DNA profiling kits means that it is possible to generate DNA profiles from very small amounts of cellular material. As a consequence, it has been shown that DNA we detect may not have arisen from a direct contact with an item, but rather through one or more intermediaries. Naturally the questions arising in court, particularly when considering trace DNA, are of how DNA may have come to be on an item. While scientists cannot directly answer this question, forensic biological results can help in discriminating between alleged activities. Much experimental research has been published showing the transfer and persistence of DNA under varying conditions, but as of yet the results of these studies have not been combined to deal with broad questions about transfer mechanisms. In this work we use published data and Bayesian networks to develop a statistical logical framework by which questions of transfer mechanism can be approached probabilistically. We also identify a number of areas where further work could be carried out in order to improve our knowledge base when helping to address questions about transfer mechanisms. Finally, we apply the constructed Bayesian network to ground truth known data to determine if, with current knowledge, there is any power in DNA quantities to distinguish primary and secondary transfer events.
authors.affiliation: Forensic Science South Australia, 21 Divett Place, Adelaide, SA 5000, Australia; School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia. Electronic address: Duncan.Taylor@sa.gov.au.
authors.forename: Duncan
authors.initials: D
authors.lastname: Taylor
authors.affiliation: Faculty of Law, Criminal Justice and Public Administration, School of Criminal Justice, University of Lausanne, 1015 Lausanne-Dorigny, Switzerland.
authors.forename: Alex
authors.initials: A
authors.lastname: Biedermann
authors.affiliation: Faculty of Law, Criminal Justice and Public Administration, School of Criminal Justice, University of Lausanne, 1015 Lausanne-Dorigny, Switzerland.
authors.forename: Lydie
authors.initials: L
authors.lastname: Samie
authors.affiliation: Faculty of Law, Criminal Justice and Public Administration, School of Criminal Justice, University of Lausanne, 1015 Lausanne-Dorigny, Switzerland.
authors.forename: Ka-Man
authors.initials: KM
authors.lastname: Pun
authors.affiliation: Faculty of Law, Criminal Justice and Public Administration, School of Criminal Justice, University of Lausanne, 1015 Lausanne-Dorigny, Switzerland; Fondation pour la Formation Continue UNIL-EPFL, University of Lausanne, 1015 Lausanne-Dorigny, Switzerland.
authors.forename: Tacha
authors.initials: T
authors.lastname: Hicks
authors.affiliation: Faculty of Law, Criminal Justice and Public Administration, School of Criminal Justice, University of Lausanne, 1015 Lausanne-Dorigny, Switzerland.
authors.forename: Christophe
authors.initials: C
authors.lastname: Champod
mesh_terms: D004247:DNA / Q000032:analysis* / Q000235:genetics; D016172:DNA Fingerprinting; D006801:Humans; D016013:Likelihood Functions; D013499:Surface Properties; D014110:Touch
chemical_list: D004247:DNA
keywords: Activity level propositions; Bayesian networks; Data; Likelihood ratio; Primary transfer; Secondary transfer