University of Cambridge > > Isaac Newton Institute Seminar Series > Bayes & the Blame Game: How to ease the mutually felt frustration between law professionals and scientists.

Bayes & the Blame Game: How to ease the mutually felt frustration between law professionals and scientists.

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FOSW01 - The nature of questions arising in court that can be addressed via probability and statistical methods

Not enough meaningful communication is taking place between the scientific community and the judiciary. Usually scientists start the dialogue by pointing out to judges and prosecutors that they utterly lack the skills needed to find the truth in criminal cases. Remarkably, not all judges and prosecutors are happy to accept this message right away. To make things worse, they are told that they can only cure their ignorance by swallowing some very distasteful medication, brewed from such dark ingredients as numbers and probability theorems. Naturally they tend to show a certain resistance. This leads some experts to the conclusion that the judiciary is unwilling and/or unable to listen to reason.

But that’s unfair. As a teacher to the judiciary and expert witness in criminal cases I’ve noticed that the majority of judges and prosecutors are intelligent and conscientious people who are willing to put a lot of effort into understanding what math and science have to offer. Unfortunately, after they learn the basics of probabilistic reasoning, it is very hard for them to get any further help when they try to apply this new, scientific way of reasoning to actual criminal cases in their daily practice. In my opinion judges and prosecutors won’t make the transition from confirmative thinking to Bayesian methods, unless they see convincing examples of complete Bayesian analyses of complicated criminal cases, including the construction of meaningful hypotheses, the choice of sensible priors, actual estimates of all likelihoods involved, and a final calculation of the posterior, including realistic uncertainties. But that’s something  most experts scare away from. Rather they – correctly – explain to the court why it’s so hard to report anything about priors or to give an opinion on e.g. the dependency of findings. Judges usually end up with just a few isolated LRs in their hands and a lot of questions on their minds.   

Now it’s the judiciary’s turn to get frustrated: Scientists keep telling that law professionals are stupid and ignorant, but apparently science doesn’t have a solution either.

How can we solve this? In my talk I will present some thoughts, based on my discussions with forensic experts, and on my contacts with a small but growing group of Dutch judges, prosecutors and police who are cautiously beginning to accept Bayesian reasoning. I will discuss some ideas on how to deal with the considerable risks involved with presenting Bayesian analyses to the courts, and present some examples from my own Bayesian reporting. Finally I’ll allow myself to dream up some over-optimistic visions of the future.  

This talk is part of the Isaac Newton Institute Seminar Series series.

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