Evaluation of forensic DNA traces when propositions of interest relate to activities: Analysis and discussion of recurrent concerns

Alex Biedermann, Christophe Champod, Graham Jackson, Peter Gill, Duncan Taylor, John Butler, Niels Morling, Tacha Hicks, Joelle Vuille, Franco Taroni

    Research output: Contribution to journalArticlepeer-review

    38 Citations (Scopus)
    34 Downloads (Pure)


    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.

    Original languageEnglish
    Article number215
    Number of pages12
    JournalFrontiers in Genetics
    Publication statusPublished - 12 Dec 2016

    Bibliographical note

    Copyright © 2016 Biedermann, Champod, Jackson, Gill, Taylor, Butler, Morling, Hicks, Vuille and Taroni. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.


    • Hierarchy of propositions
    • Interpretation
    • Probability assignment
    • Probative value


    Dive into the research topics of 'Evaluation of forensic DNA traces when propositions of interest relate to activities: Analysis and discussion of recurrent concerns'. Together they form a unique fingerprint.

    Cite this