On the benefits and pitfalls of using the likelihood ratio to help understand the impact of forensic evidence
In general the likelihood ratio (LR) is a very good and simple method for communicating the impact of evidence, but its correct use is based on strict assumptions that have been routinely ignored by forensic experts and statisticians, leading to the very kind of confusion and misunderstanding (e.g. when presented to lawyers and juries) that it was supposed to help avoid. This talk will highlight the problems which invalidate the LR, and will show how they can be avoided by incorporating all relevant information in a Bayesian network.
Norman Fenton is Professor of Risk Information Management at Queen Mary London University and is also a Director of Agena Ltd. Norman’s works on quantitative risk assessment typically involves analysing and predicting the probabilities of unknown events using Bayesian statistical methods including especially causal, probabilistic models (Bayesian networks). This type of reasoning enables improved assessment by taking account of both statistical data and also expert judgment. Norman has a special interest in raising public awareness of the importance of probability theory and Bayesian reasoning in everyday life (including how to present such reasoning in simple lay terms) and he maintains a website dedicated to this and also a blog focusing on probability and the law. In March 2015 Norman presented the BBC documentary Climate Change by Numbers. Norman has published 7 books and over 200 referred articles and has provided consulting to many major companies world-wide. Norman's current projects are focused on using Bayesian methods for improved legal reasoning and improved medical decision making.