Towards source level evaluation of the evidential value of fibre examinations. (May 2015)

• Record Type: Journal Article
• Authors: Vooijs, Cees; Vergeer, Peter; van der Weerd, Jaap
• Is Part Of: Forensic science international. Volume 250(2015)
• Page Start: 57
• Page End: 67
• Publication Date: 2015-05
• Subjects: Fiber evidence -- Numerical evaluation -- Match -- Likelihood ratio LR -- Discrimination study -- Discrimination power -- Population study; Medical jurisprudence -- Periodicals; Chemistry, Forensic -- Periodicals; Forensic Medicine -- Periodicals; Médecine légale -- Périodiques; Chimie légale -- Périodiques; Gerechtelijke geneeskunde; Gerechtelijke chemie; Gerechtelijke psychiatrie; Chemistry, Forensic; Medical jurisprudence; Electronic journals; Periodicals; Electronic journals; 614.1
• DOI: 10.1016/j.forsciint.2015.02.009
• Languages: English
• ISSNs: 0379-0738

Abstract

Highlights: A review of studies on the discrimination of fibres is provided. A statistical model for source level interpretation of fibre examination is proposed. Source level evidential value is calculated for four scenario's. The assumptions needed for numerical evaluation are detailed. Future developments needed for a justified path towards numerial evaluation are detailed. Abstract: This paper aims to provide the first steps towards a numerical source level evaluation of fibre evidence. For that purpose, likelihood ratio equations are derived for four generic scenarios, in which the source frequency, the number of references and trace types investigated, and the number of matches vary. Previous experimental studies into the evaluation of fibre evidence are reviewed and we demonstrate how the results of these studies, as well as other data, can be used to evaluate the derived equations for the four scenarios. Evaluation is not straightforward and requires a number of assumptions. This is mainly because the relevant population under consideration in a specific case cannot be sufficiently evaluated. In addition, the subjective match-criterion in current forensic fibre examinations makes it impossible to implement a good evaluation of the within-variation of samples. As a result, the discrimination power, currently calculated for discrimination studies, is only valid for samples with negligible heterogeneity. We conclude that reporting a numerical evidential value for forensic fibre examinations is not yet feasible as the data are available for only a few types of fibres and cannot be used without several assumptions. We propose a number of developments that are required to improve the accuracy and numerical analysis.