Update on the use of Bayes in the Netherlands Appeal Court

In July I reported about the so-called Breda 6 case in the Netherlands and how a Bayesian argument was presented in the review of the case. My own view was that the Bayesian argument was crying out for a Bayesian network representation (I provided a model in my article to do that).

Now Richard Gill has told me the following:

Finally there has been a verdict in the 'Breda 6' case. The suspects were (again) found guilty. The court is somewhat mixed with respect to the Bayesian analysis: On the one hand they ruled that Frans Alkmeye had the required expertise, and that he was rightly appointed as a 'Bayesian expert'. On the other hand they ruled that a Bayesian analysis is still too controversial to be used in court. Therefore they disregarded 'the conclusion' of Frans's report. This is a remarkable and unusual formulation in verdicts, the normal wording is that report has been disregarded.

This unusual wording is no accident: If the court would say that they had disregarded the report, they would lie, since actually quite a lot of the Bayesian reasoning is included in their judgment. A number of considerations from Frans's report are fully paraphrased, and sometimes quoted almost verbatim.

Also I noticed that the assessment of certain findings is expressed in a nicely Bayesian manner.

However: Contrary to Frans's assessment, the court still thinks that the original confessions of three of the suspects contain strong evidence. Unfortunately, the case is not yet closed, but has been taken to the high court.

Frans Alkmeye has also been appointed as a Bayesian expert in yet another criminal case.

The ruling that the Bayesian analysis is too controversial is especially disappointing since we have recently been in workshops with Dutch judges who are very keen to use Bayesian reasoning - and even Bayesian networks (in the Netherlands there are no juries so the judges really do have to make the decisions themselves). These judges - along with Frans Alkemade - will be among many of the world's top lawyers, legal scholars, forensic scientists, and mathematicians participating in the Isaac Newton Institute Cambridge Programme on Probability and Statistics in Forensic Science that will take place July-Dec 2016. This is a programme that I have organised along with David Lagnado, David Balding, Richard Gill and Leila Schneps. It derives from our Bayes and the Law consortium which states that, despite the obvious benefits of using Bayes:

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.

One of the core objectives of the 6-month programme is to address this issue thoroughly. Within the programme there are 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