Demonstrating Reliability and Directing Scrutiny: as framework to assist scientists and lawyers

  • Sophie Carr (Speaker)
  • Piasecki, E. (Speaker)
  • Gillian Tully (Speaker)
  • Angela Gallop (Speaker)

Activity: Talk or presentationOral presentation


In recent decades, forensic science evidence has come to play an increasingly significant role in criminal proceedings. However, the attention paid within criminal justice systems to the validity and reliability of the evidence has not maintained pace, despite international scrutiny from scientists, statisticians, governments and those involved in law reform. It is evident that the parameters of a) some case specific interpretations, and b) those relating to different forensic disciplines remain elusive to some legal practitioners.

These are not issues restricted to individual jurisdictions; they are universal - as evidenced by the Scottish Fingerprint Inquiry and the US President’s Council of Advisors on Science and Technology (PCAST). It is therefore essential that within the context of national, and increasingly international, criminal investigations, forensic practices and scientists convey the evidential value of the scientific findings in a manner that is understandable and useable to all. Forensic experts must be alert to the fact that those in the legal profession, who have no scientific training, may be ill-equipped to deal effectively with scientific evidence and are at risk of making uninformed assumptions of reliability. There is a need for a clear and transparent framework capable of illustrating the validity of an expert’s opinion, satisfying legal jurisdictional needs and reducing the potential for miscarriages of justice.

In order to assist both experts and legal professionals, the authors conceptualise the reliability of evidence as a continuum rather than a binary process, with contested ‘liminal’ zones marking areas of transition where heightened scrutiny may be required to demonstrate the validity of an expert’s opinion. This paper will signal where, and how, additional scrutiny and information should be conveyed to ensure (i) scientists can and do demonstrate that their case specific opinion is reliable and (ii) the legal professions are alert to the scientific validity underpinning the opinion of the forensic expert. To facilitate this we offer a structured, tripartite conception of scientific validity. Extending PCAST’s dual requirements for scientific rigour, exemplified through foundational and applied validity, we propose a third criterion of evaluative validity. Focusing on concluding opinions, evaluative validity considers the underpinning disciplinary knowledge directly informing the expert’s inferential reasoning and interpretation of evidential strength in the instant case. This proposed tripartite framework thereby constitutes a powerful methodology, drawing attention to subjective factors and potential pressure points, which require greater critique as the evidence enters the ‘liminal zone’ for reliability. All three elements of this validity framework should be sufficiently visible to lawyers and judges to inform and warrant an attitude of ‘critical trust’ on their behalf in respect of the expert’s evidence.
Period20 Aug 2018
Event titleEuropean Association of Forensic Sciences 2018: 2020: The Forensic Odyssey
Event typeConference
LocationLyon, FranceShow on map
Degree of RecognitionInternational