The Bayesian approach to forensic evidence: Evaluating, communicating, and distributing responsibility

Abstract

This article draws attention to communication across professions as an important aspect of forensic evidence. Based on ethnographic fieldwork in the Swedish legal system, it shows how forensic scientists use a particular quantitative approach to evaluating forensic laboratory results, the Bayesian approach, as a means of quantifying uncertainty and communicating it accurately to judges, prosecutors, and defense lawyers, as well as a means of distributing responsibility between the laboratory and the court. This article argues that using the Bayesian approach also brings about a particular type of intersubjectivity; in order to make different types of forensic evidence commensurable and combinable, quantifications must be consistent across forensic specializations, which brings about a transparency based on shared understandings and practices. Forensic scientists strive to keep the black box of forensic evidence – at least partly – open in order to achieve this transparency.