The Logic of Inference and Decision for Scientific Evidence

Uncertainty is an inevitable complication encountered by members of the judiciary who face inference and decision-making as core aspects of their daily activities. Inference, in this context, is mainly inductive and relates to the use of incomplete information, to reason about propositions of interest. Applied to scientific evidence, this means, for example, to reason about whether or not a person of interest is the source of a recovered evidential material and factfinders are required to make decisions about ultimate issues, for example, regarding a defendant’s guilt. The role of forensic scientists, whose duty is to help assess the probative value of scientific findings, is to offer to mandate authorities’ conclusions that are scientifically sound and logically defensible. This chapter lays out the fundamentals of inference and decision-making under uncertainty with regard to forensic evidence. The authors explicate explain the subjectivist version of Bayesianism and analyze the usefulness of the likelihood ratio in for measuring the degree to which the evidence discriminates between competing propositions in a trial. They also underscore emphasize the importance of decision analysis as a framework that forces helps decision-makers to formalize preference structures.