Expressing evaluative forensic science opinions in a court of law

Abstract

Forensic science evidence must be presented in a form that can be accommodated within the process of proof employed by judges and juries. This is a non-mathematical inductive process that seeks 'the inference to best explanation' to a standard of proof beyond reasonable doubt. The question posed is not the mathematical probability of the prosecution hypothesis but whether having regard to all the evidence before the court the prosecution hypothesis is the only explicable hypothesis, in the sense that no reasonably possible defence hypothesis remains open. The challenge is to present forensic science evidence in a form that can be accommodated within this non-mathematical inductive standard of proof. It is argued that this is most effectively achieved if that evidence is tendered as a frequency rather than as a likelihood ratio. © The Author [2012]. Published by Oxford University Press. All rights reserved.