Medicine and the law: what’s happening?

Conviction by mathematical error?

An editorial in the BMJ has urged doctors to take responsibility for the quality of expert evidence being given in courts. ‘Even more problematic than the issue of presenting statistical evidence fairly is the problem of getting it wrong’, wrote Stephen Watkins, Director of Public Health, Stockport Health Authority, UK.

The author described how he considered mathematical error contributed to the conviction of solicitor Sally Clark for smothering her two infant children. An eminent paediatrician gave evidence that the chances of two cot deaths happening in this family was ‘vanishingly small’ – 1 in 73 million. However, according to the Dr Watkins, the prosecution used the figure of 1 in 73 million rather than 1 in 2.75 million (the risk for the whole population) because of the family’s affluence.