Statistics and the expert witness

This chapter considers the use of statistics within forensic science, especially its relevance to the interpretation of evidence, and presentation of that interpretation to the court of law. It looks at the areas in which the expert witness and statistics interact, and the responsibilities of the expert witness in relation to those interactions using examples from court cases to illustrate some issues which have been encountered. An expert witness presents evidence and opinion on a field in which they hold expertise through study and research, and that their expertise has to be beyond that which is expected of a member of the jury. The Appeal Court has issued guidance for practitioners, experts and the judiciary in English courts, where their concern is for the introduction of Bayes’ theorem as evidence because of its potential to confuse the fact-finder and thus lead to miscarriages of justice.