title: Evaluation of Forensic DNA Traces When Propositions of Interest Relate to Activities: Analysis and Discussion of Recurrent Concerns.
abstract: When forensic scientists evaluate and report on the probative strength of single DNA traces, they commonly rely on only one number, expressing the rarity of the DNA profile in the population of interest. This is so because the focus is on propositions regarding the source of the recovered trace material, such as "the person of interest is the source of the crime stain." In particular, when the alternative proposition is "an unknown person is the source of the crime stain," one is directed to think about the rarity of the profile. However, in the era of DNA profiling technology capable of producing results from small quantities of trace material (i.e., non-visible staining) that is subject to easy and ubiquitous modes of transfer, the issue of source is becoming less central, to the point that it is often not contested. There is now a shift from the question "whose DNA is this?" to the question "how did it get there?" As a consequence, recipients of expert information are now very much in need of assistance with the evaluation of the meaning and probative strength of DNA profiling results when the competing propositions of interest refer to different activities. This need is widely demonstrated in day-to-day forensic practice and is also voiced in specialized literature. Yet many forensic scientists remain reluctant to assess their results given propositions that relate to different activities. Some scientists consider evaluations beyond the issue of source as being overly speculative, because of the lack of relevant data and knowledge regarding phenomena and mechanisms of transfer, persistence and background of DNA. Similarly, encouragements to deal with these activity issues, expressed in a recently released European guideline on evaluative reporting (Willis et al., 2015), which highlights the need for rethinking current practice, are sometimes viewed skeptically or are not considered feasible. In this discussion paper, we select and discuss recurrent skeptical views brought to our attention, as well as some of the alternative solutions that have been suggested. We will argue that the way forward is to address now, rather than later, the challenges associated with the evaluation of DNA results (from small quantities of trace material) in light of different activities to prevent them being misrepresented in court.
authors.affiliation: Faculty of Law, Criminal Justice and Public Administration, School of Criminal Justice, University of Lausanne Lausanne, 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 Lausanne, Switzerland.
authors.forename: Christophe
authors.initials: C
authors.lastname: Champod
authors.affiliation: School of Science, Engineering and Technology, Abertay University Dundee, Scotland.
authors.forename: Graham
authors.initials: G
authors.lastname: Jackson
authors.affiliation: Norwegian Institute of Public HealthOslo, Norway; Department of Forensic Medicine, University of OsloOslo, Norway.
authors.forename: Peter
authors.initials: P
authors.lastname: Gill
authors.affiliation: Forensic Science South AustraliaAdelaide, SA, Australia; School of Biological Sciences, Flinders UniversityAdelaide, SA, Australia.
authors.forename: Duncan
authors.initials: D
authors.lastname: Taylor
authors.affiliation: National Institute of Standards and Technology Gaithersburg, MD, USA.
authors.forename: John
authors.initials: J
authors.lastname: Butler
authors.affiliation: Section of Forensic Genetics, Department of Forensic Medicine, Faculty of Health and Medical Sciences, University of Copenhagen Copenhagen, Denmark.
authors.forename: Niels
authors.initials: N
authors.lastname: Morling
authors.affiliation: Faculty of Law, Criminal Justice and Public Administration, School of Criminal Justice, University of Lausanne Lausanne, Switzerland.
authors.forename: Tacha
authors.initials: T
authors.lastname: Hicks
authors.affiliation: Faculty of Law, University of Neuchâtel Neuchâtel, Switzerland.
authors.forename: Joelle
authors.initials: J
authors.lastname: Vuille
authors.affiliation: Faculty of Law, Criminal Justice and Public Administration, School of Criminal Justice, University of Lausanne Lausanne, Switzerland.
authors.forename: Franco
authors.initials: F
authors.lastname: Taroni
keywords: hierarchy of propositions; interpretation; probability assignment; probative value