Bayes Factor for Evaluative Purposes

AbstractThis chapter presents and discusses the use of the Bayes factor for the evaluation of scientific evidence in the form of discrete, continuous and continuous multivariate data. The latter may present a complex dependence structure that will be handled by means of multilevel models. The notion of “evaluative purpose” is understood here as referring to situations in which material of known source (control material) and evidential material of unknown source (recovered or questioned material) is collected and analyzed. The purpose is to evaluate the effect of the output of the examinations, in the form of scores or measurements of features, on the odds in favor of a proposition put forward by the prosecution, compared to an alternative proposition advanced by the defence. A discussion is included of the sensitivity of the described Bayes factor procedures to changes in the features of recovered and control materials, the available background information, as well as to choices made during probabilistic modelling and prior elicitation.