The impact of commercialization on the evaluation of DNA evidence

BACKGROUND Guidance on designing cost-effective examinations and on interpretation of expert observations has been available since the late 1990s in the form of a model framework called Case Assessment and Interpretation (CAI) (Cook et al., 1998a,b; Jackson and Jones, 2009). The underlying principles of the guidance were subsequently encoded in a published standard written by the Association of Forensic Science Providers (AFSP, 2009) and have been incorporated in draft guidance from the European Network of Forensic Science Institutes (ENFSI). The guidance is predicated on a logical approach to the evaluation of evidence, requiring examiners to have an understanding and acceptance of the laws of probability. A key element in such an evaluation is the assessment of a likelihood ratio (LR) as the basis of providing logical, balanced, robust, expert opinion. In addition to the use of an LR approach, a second notion, that of the hierarchy of issues, is a vital element of evaluation. The hierarchy of issues is a scheme that helps identify the case issue that the expert evidence is addressing and thereby clarifies the contribution that evidence is making to the judicial process (Cook et al., 1998b; Evett et al., 2000; Jackson et al., 2006). Using the hierarchy, case issues are classified as belonging to one of four levels—“offence,” “activity,” “source,” or “sub-source” (Jackson, 2009). This article discusses how commercialization of forensic services, whilst not posing any immediate threat to an evaluation of an LR for scientific evidence, does pose a risk of misleading evidence being adduced if the issue being addressed by the scientist is at too low a level in the hierarchy of issues.