The decisionalization of individualization

Abstract

Throughout forensic science and adjacent branches, academic researchers and practitioners continue to diverge in their perception and understanding of the notion of 'individualization', that is the claim to reduce a pool of potential donors of a forensic trace to a single source. In particular, recent shifts to refer to the practice of individualization as a decision have been revealed as being a mere change of label [1], leaving fundamental changes in thought and understanding still pending. What is more, professional associations and practitioners shy away from embracing the notion of decision in terms of the formal theory of decision in which individualization may be framed, mainly because of difficulties to deal with the measurement of desirability or undesirability of the consequences of decisions (e.g., using utility functions). Building on existing research in the area, this paper presents and discusses fundamental concepts of utilities and losses with particular reference to their application to forensic individualization. The paper emphasizes that a proper appreciation of decision tools not only reduces the number of individual assignments that the application of decision theory requires, but also shows how such assignments can be meaningfully related to constituting features of the real-world decision problem to which the theory is applied. It is argued that the decisonalization of individualization requires such fundamental insight to initiate changes in the fields' underlying understandings, not merely in their label.

Normative decision analysis in forensic science

“…or 'what to report?'. One of the viewpoints that we reiterate in this discussion paper is that such questions can be understood as decisions, and hence looked at through the formal theory of decision (Biedermann et al, 2008(Biedermann et al, , 2016aTaroni et al, 2010).…”

“…The last section of the paper, Section 5, will discuss the value and practical impact of probabilistic decision theory (i.e., expected value theory) in forensic science and draw parallels to legal principles (e.g., the notion of 'balance of probabilities'). The paper is didactic in Sections 2 to 4, providing an overview of perspectives and more detailed developments previously presented in Biedermann et al (2008Biedermann et al ( , 2014Biedermann et al ( , 2016a and Taroni et al (2010). Discussions presented in Sections 5 and 6 provide a position statement on the extent to which decision-theoretic insight might meaningfully contribute to ongoing reforms of forensic reporting practice and the interface between forensic science and legal practitioners.…”

“…In a generalized decisiontheoretic reformulation, the 'balance of probability' standard would extend to, for example, 'the balance between probabilities and losses for adverse decision consequences' or 'the balance of probability moderated by the losses for adverse decision consequences'. The inherent mechanical perspective of the latter formulation can further be illustrated by translating the formulaic result (4) in graphical terms of a physical law, such as Archimedes' Law of Lever (Biedermann et al, 2016a). This law states that an equilibrium is established between two magnitudes if their distances are, with respect to a point of suspension, reciprocally proportional to their weights (e.g., Dijksterhuis et al, 1987).…”

Letter to the Editor—Commentary on: Dror IG, Langenburg G. “Cannot decide”: The Fine Line Between Appropriate Inconclusive Determinations Versus Unjustifiably Deciding not to Decide. J Forensic Sci https://doi.org/10.1111/1556-4029.13854. Epub 2018 Jul 5

“…We may also prefer a missed identification (i.e., not identifying a person of interest who is actually the source of the crime mark), even though being an inaccurate decision consequence, to a false identification. Now imagine, for the purpose of illustration, that we have a high aversion to false identifications, for whatever reason (e.g., policy matters), 4 or we may even want to avoid false identifications altogether. Especially in the latter case, it will be sensible for us not to identify, despite a high probability for the proposition that the person of interest is the source of the crime mark and/or the fact that we assign a high probative value to the fingermark comparison.…”

“…7 Weight of evidence may only be said to be "lost" if we do not use it for its intended purpose: that is, if we do not use it to revise our beliefs about the propositions of interest. 4 A further issue that Dror and Langenburg raise is the question of "(. .…”