This CSAFE Center Wide webinar was presented on January 7, 2019 by Dr. Danica Ommen, CSAFE researcher and Assistant Professor at Iowa State University. Dr. Ommen has provided presentation slides for Part 1 and Part 2 and references.
In this two-part presentation, we will focus on aspects of the forensic identification of source problems where the main question of interest is determining the origin of evidence with unknown source. In order to solve this problem, we need to determine the value of the evidence with respect to two competing propositions for its origin by computing some type of “likelihood ratio.” After we get this value of evidence, the idea is that it can be used to help someone make a decision. In the case of a criminal trial, the decision would be regarding the guilt or innocence of the defendant. However, there are many different ideas about what the “likelihood ratio” should look like and how to compute its value, especially in the face of uncertainty. Often, we are uncertain about the statistical models we’ve chosen to describe the evidence. In this presentation, we will discuss the basic definitions, as well as various computational strategies, for both the weight and the value of evidence. In addition, we will review and discuss recent controversies surrounding the value of evidence.