Academic journal article University of Queensland Law Journal

Performance Claims in Forensic Science Expert Opinion Evidence

Academic journal article University of Queensland Law Journal

Performance Claims in Forensic Science Expert Opinion Evidence

Article excerpt

I INTRODUCTION

Expert opinions provided by forensic examiners are used to help establish the facts of a case. Forensic science opinion evidence, with the exception of DNA, has gone largely unchallenged in court since its inception. (1) Several recent authoritative reports, however, have questioned the epistemic claims made by forensic examiners, and have highlighted the frequent absence of solid scientific research demonstrating the validity, reliability and accuracy of forensic analyses. (2) These reports, along with commentary in the broader scientific community, (3) include recommendations for the urgent development of quantifiable measures of human performance in forensic pattern-matching.

Legal scholars have argued that in order for fact-finders to rationally evaluate forensic evidence they need information about the validity and reliability of forensic science techniques, including the limitations, proficiency and indicative error rates of forensic examiners' conclusions. (4) In this article, we contend that in order to fulfil the need for empirical testing of human matching-performance, and to provide this information to fact-finders, we first need to know what performance claims are being made by forensic examiners. Without reasonable and precise claims about ability and levels of performance, empirical studies cannot be designed and conducted. We will attempt to illuminate the claims made by forensic examiners by surveying the accessible professional literature across four forensic disciplines. We will then interpret these claims in terms of their amenability to empirical testing, and suggest a path forward for the forensic pattern-matching disciplines.

II BACKGROUND

In the past decade, several authoritative reports have emerged that describe a situation in which very little is known about the validity and reliability of forensic science evidence. In 2009, the United States National Academy of Science ('NAS') issued a report highlighting the absence of scientific evidence underpinning the forensic disciplines and the evidence provided by expert witnesses in court. (5) A Scottish Inquiry and a United States National Institute of Justice Report both highlight the inevitability of human error in forensic examinations. (6) A 2016 report from the United States President's Council of Advisors on Science and Technology (7) ('PCAST') reiterated the concern that forensic science lacks a strong scientific underpinning. In particular, the report focused on the lack of evidence supporting the scientific validity and reliability of the forensic feature-comparison disciplines. The term 'forensic feature-comparison methods' is used in the PCAST Report in reference to

the wide variety of methods that aim to determine whether an 
evidentiary sample (eg, from a crime scene) is or is not associated 
with a potential source sample (eg, from a suspect) based on the 
presence of similar patterns, impressions, features, or characteristics 
in the sample and the source. (8)

The report specified the need for empirical evidence showing that forensic disciplines conform to scientific standards for foundational validity--whether evidence is based on reliable principles and methods. The report also insisted that evidence is needed to show that forensic disciplines conform to scientific standards for applied validity--whether examiners reliably apply the principles and methods. (9) As the methods used in the feature-comparison disciplines depend upon human judgements to make evidentiary conclusions, evidence of foundational and applied validity needs to show that human judgement does indeed reliably produce accurate conclusions.

Examiners in the forensic feature-comparison disciplines are the 'instruments of analysis' (10) who deploy perceptual expertise in order to make judgements about forensic evidence. (11) Regardless of the object of examination (eg fingerprints, footwear, tyre tracks), forensic feature-comparison examiners engage in a cognitive process to evaluate the visual similarity between marks left at a crime scene and marks of known origins. …

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