Statistic and The Law


Nineteenth Annual Darwin College Lecture Series 2004

Lecture 7   :   February 27th 2004

Philip Dawid

Pearson Professor of Statistics at University College London



Recent cases involving multiple infant deaths and DNA profiling identification have highlighted some of the problematic issues that can arise when statistical evidence is introduced into legal proceedings. It might appear that the concerns of Statistics and those of Law have little common ground, but in fact both disciplines address the same fundamental task: the drawing out of sound inferences from evidence. I will describe the logic of probabilistic reasoning and its application to cases at law, and show how its all too frequent neglect or misapplication has led to serious errors and miscarriages of justice.

Both Statistics and Law are faced with the problem of structuring and making sense of mixed masses of evidence. The modern technology of "Probabilistic Expert Systems" can be seen as an extension of the century-old "Wigmore chart" method, used by lawyers to organise the many items of evidence in a case and express the many kinds of relationship between them. This technology is now being used to provide a correct and efficient way of taking account of whatever limited evidence may be at hand, a task that could otherwise be impossible. An important area of application is the interpretation of DNA profiles taken from relatives when that of the suspect (in a criminal case) or putative father (in a paternity case) is unavailable.

Finally I shall discuss the wider relevance of the use of formal methods of reasoning about evidence, in the context of an inter-disciplinary programme on "Evidence, Inference and Enquiry".


Philip Dawid is Pearson Professor of Statistics at University College London. He has published around 120 research papers on theoretical and applied statistics. His jointly authored book em Probabilistic Networks and Expert Systems won the 2002 DeGroot Prize for a Published Book in Statistical Science. In 2000 he served as President of the International Society for Bayesian Analysis.

In 1966, following a first degree in Mathematics, Philip Dawid joined Darwin College Cambridge as one of its first graduate students, studying for a Diploma in Mathematical Statistics. Naively expecting this to open up lucrative employment opportunities, he found himself fascinated by the logical challenges and ferocious controversies pervading the subject, and became an academic instead. He was rapidly converted to the subjective approach to probability and statistics pioneered by the 18th Century nonconformist minister Thomas Bayes, and has since used this as a basis for his wide-ranging investigations into the foundations and applications of reasoning under uncertainty.

He has long had an active interest in the structuring and interpretation of legal evidence. This has led to service as an expert witness or adviser in a number of court cases, including the recent case of Sally Clark. He currently heads an international team of statisticians, mathematicians, epidemiologists and forensic scientists who are developing Bayesian expert systems to solve complex cases of forensic identification from DNA profiles.

These legally inspired investigations have also highlighted the many logical subtleties and pitfalls that beset evidential reasoning more generally. To address these he has this year established a multidisciplinary research programme on Evidence, Inference and Enquiry at University College London. This is bringing together researchers from a wide diversity of disciplinary backgrounds to seek out common ground, to advance understandings, and to improve the handling of evidence. 

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