Probabilistic reasoning in the law. Part 1: Assessment of probabilities and explanation of the value of DNA evidence.

Problems associated with the interpretation of DNA evidence are investigated with reference to measures of uncertainty associated with the presentation of such evidence in an adversarial context. The use of probabilistic arguments associated with expert scientific testimony and cases where DNA evidence has been presented in court are studied. A series of problems were developed for, and given to, forensic medicine students, forensic science students and practitioners (advocates and forensic scientists) in Scotland to investigate their understanding of uncertainty. In the first part, four different methods of presentation of the value of DNA evidence were given to the participants and their responses are described. In the second part, different explanations of the value of DNA evidence as given by experts in court were given to the participants and their responses are described. The authors suggest improvements for the presentation of scientific evidence and for the education of future lawyers and forensic scientists.