RSS sections and groups meeting reports

Merseyside local group meeting: Legal and forensic statistics

Written by Dr Laura Bonnett on . Posted in Sections and local group meeting reports

On 3rd May 2016, the RSS Merseyside local group hosted a fascinating afternoon session on legal and forensic statistics. There were 23 people in attendance, the majority of whom were RSS members. As usual, most attendees were from the University of Liverpool. However, there were also visitors from Liverpool Hope University, University Hospital of South Manchester, and the Health and Safety Executive.

Professor Jane Hutton from the Department of Statistics at the University of Warwick began the afternoon with an excellent insight into the life of a civil expert witness. She began by clarifying that a civil case is one which does not involve the police or the state. She then raised issues regarding the need for good data which is both accurate and up-to-date in order to make informed decisions, and then talked through two of her previous cases; giving interesting awareness of the differences between countries, and even between Scottish and English law.

Jane is keen to recruit more statisticians to be civil expert witnesses, and is happy to talk to interested people further if they think it would appeal to them. Apparently, critical appraisal of journal articles, and basic statistical understanding are the main requirements!

Professor Colin Aitken from the School of Mathematics at the University of Edinburgh spoke next. Being actively involved with criminal law, rather than civil cases, he began with the history of statistics in court and proceeded to talk through the use of likelihood ratios which balance prosecution and defence propositions, with evidence and a framework of circumstances.

Colin then explained the statistics behind the Sally Clark case - Sally was imprisoned for killing her two infants as the court thought the chance of two deaths within one family due to Sudden Infant Death Syndrome (SIDS) was too small to be believable. However, Colin proved that in fact the chance of two SIDS death within one family was much higher than the two children having been murdered by a parent.

Colin’s final example involved cocaine on bank notes – he revealed that there are traces of cocaine on about 90% of bank notes. Therefore it is very challenging to calculate if the bank notes are associated with a person involved with cocaine related criminal or not.

After Colin’s talk, Gabriela Czanner (chairman of the RSS Merseyside Local Group) chaired a panel discussion with the two speakers. Questions included whether courts were interested in just point estimates, or confidence intervals too, and what the benefits or not were of these scenarios. Questions were also raised regarding the statistical education of lawyers, barristers and judges so that they are better able to understand the material from an expert witness.

Feedback from the session suggested that people had really enjoyed the afternoon, particularly getting to hear about a relatively unknown area of statistics. Many of the group said they would look out for future meetings of the RSS Statistics in Law section, especially the one scheduled for later this year in Manchester.

The next meetings of the RSS Merseyside Local Group relate to joint modelling with Virginie Rondeau and speakers from the University of Liverpool, and 'fair standings' in English and other European professional football leagues with David Firth. Full details will be announced in due course.

Merseyside local group

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