Bayes and the Law: About

Why Bayes and the law?

Bayesian reasoning (which incorporates the likelihood ratio and Bayes’ theorem) is a logical framework for reasoning about uncertainty. Experts (including statisticians and forensic scientists) have argued for many years that Bayesian reasoning has the potential to improve the efficiency, transparency and fairness of the justice system, and to avoid the kind of fallacies in probabilistic reasoning that have not only troubled the appellate courts but are also likely to have misled tribunals of fact in many trials.

The use of Bayesian reasoning in investigative and evaluative forensic science and the law is, however, the subject of much confusion. It is deployed in the adduction of DNA evidence, but expert witnesses and lawyers struggle to articulate the underlying assumptions and results of Bayesian reasoning in a way that is understandable to lay people.  The extent to which Bayesian reasoning could benefit the justice system by being deployed more widely, and how it is best presented, is unclear and requires clarification.

Who are we?

We are a multi-disciplinary consortium that includes world-class mathematicians, scientists, psychologists, legal academics and practitioners, police officers, journalists and lay people who wish to collaborate on the issues surrounding the use of probabilistic reasoning in criminal law. The consortium is run by Norman Fenton, Professor of Risk Information Management at Queen Mary, University of London (QMUL), Dr Amber Marks, Lecturer in Criminal Law and Evidence, QMUL and Dr David Lagnado (Dept Experimental Psychology, University College London).

What do we do?

Primarily we run events that attempt to improve the state-of-the-art in Bayesian/probabilistic legal reasoning and to bridge the gap between academics working in this area and practicing lawyers. Our corrent major activity revolves around the Isaac Newton Institute Cambndge Programme on Probability and Statistics in Forensic Science that will take place July-Dec 2016 (see details) organised by Norman Fenton, David Lagnado, David Balding, Richard Gill and Leila Schneps.  There are currently three scheduled workshops: 

  1. The nature of questions arising in court that can be addressed via probability and statistical methods, Tue 30th Aug 2016 - Tue 30th Aug 2016
  2. Bayesian networks in evidence analysis, Mon 26th Sep 2016 - Thurs 29th Sep 2016 
  3. Statistical methods in DNA analysis and analysis of trace evidence, Mon 7th Nov 2016 - Mon 7th Nov 2016

 For further details contact Norman Fenton (n.fenton at

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