Are Inconclusive Decisions in Forensic Science as Deficient as They Are Said to Be?

Alex Biedermann,Joëlle Vuille,Franco Taroni,Silvia Bozza

doi:10.3389/fpsyg.2019.00520

Abstract

Many quarters of forensic science use reporting formats such as “identification,” “inconclusive,” and “exclusion.” These types of conclusions express opinions as to whether or not a particular person or object is the source of the material or traces of unknown source that is of interest in a given case. Rendering an “inconclusive” conclusion is sometimes criticized as being inadequate because—supposedly—it does not provide recipients of expert information with helpful directions. In this paper, we critically examine this claim using decision theory. We present and defend the viewpoint according to which deciding to render an “inconclusive” conclusion is, on a formal account, not as inadequate as may commonly be thought. Using elements of decision theory from existing accounts on the topic, we show that inconclusive conclusions can actually be viable alternatives with respect to other types of conclusions, such as “identification.”

Highlights

When forensic scientists compare questioned material of unknown source with material from a known source, they are often faced with the question of whether the compared materials come from the same source
Especially decision analysis and decision-making, it is important to be rigorous in the use of terminology3
We will rely on expected utility to analyse and compare rival decisions. This may sound technical, but we will show that with suitable choices of the measuring scales and of a pair of consequences that are treated as benchmarks, the proposed framework simplifies considerably and becomes suitable for forensic purposes by limiting the number of choices to be made by the decision-maker during the elicitation of the utility function

Summary

Introduction

When forensic scientists compare questioned material of unknown source with material from a known source, they are often faced with the question of whether the compared materials come from the same source. A fingerprint examiner may be asked to say whether a given fingermark comes form a particular person of interest. Such conclusions are commonly known as “source identifications” (e.g., DOJ, 2018). The main criticism is that by providing such conclusions, scientists directly express opinions about propositions of interest (i.e., the proposition of common source), a task that is considered to be above and beyond their area of competence (Champod et al, 2016). Rather than expressing opinions on propositions, scientists should concentrate on the value of their findings—i.e., the results of their comparative examinations—and provide an assessment of the extent to which those findings allow one to discriminate between the various propositions of interest (Champod and Evett, 2001).

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