Sally Clark

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For other persons named Sally Clark, see Sally Clark (disambiguation).

The British solicitor Sally Clark was convicted in November 1999 for the murder of her two children, Christopher in 1996, and Harry, early in 1998, both within a few weeks of their birth. The convictions were upheld at an appeal in October 2000, but quashed in a second appeal in January 2003, because material evidence of a medical nature had come to light, which had not been available either to the trial court, or the first appeal.

The case has also been much criticised because of the way statistical evidence had been misrepresented in the original trial, particularly by expert witness Sir Roy Meadow, former Professor of Paediatrics at the University of Leeds. He stated in evidence as an expert witness that 'One sudden infant death in a family is a tragedy, two is suspicious and three is murder unless proven otherwise' and that the chances of two Sudden Infant Deaths in the same affluent, non-smoking family were 1 in 73 million. This figure came from the Confidential Enquiry for Stillbirths and Deaths in Infancy (CESDI), an authoritative and detailed study of deaths of babies in five regions of England between 1993 and 1996. The original report states that the chances of a randomly chosen baby dying a cot death are 1 in 1,303. If the child is from an affluent, non-smoking family, with the mother over 26, the odds fall to around 1 in 8,500. The authors go on to say that if there is no link between cot deaths of siblings then we would be able to estimate the chances of two children from such a family both suffering a cot death by squaring 1/8,500 - giving the figure of 1 chance in 73 million quoted by Meadow in court.

However, it should be noted this calculation is based upon a very strong assumption, namely the independence of deaths between siblings; it would not apply if there were to be a common cause of death, for example, if a genetically inherited defect was a contributory factor in the deaths. No evidence of independence was presented as evidence and more recent work by Professor Ray Hill of the Mathematics Department of the University of Salford suggests that independence is unlikely. The chances of a family which has already had a cot death having a second cot death are estimated by Hill to be around 1 in 100, not 1 in 8500.

Furthermore, if the chances of a double cot death are relevant to assessment of guilt then the chances of a double murder are also relevant and should have been presented and compared. Even if the probability of two instances of SIDS were as low as 1 in 73 million, it is not unlikely to have occurred to some family in the country. In October 2000, the Royal Statistical Society wrote a letter to the Lord Chancellor and issued a press release which pointed out some of the problems, while the appeal judges concluded "...it seems likely that if this matter had been fully argued before us we would, in all probability, have considered that the statistical evidence provided a quite distinct basis upon which the appeal had to be allowed." See Prosecutor's fallacy for a fuller analysis of these issues.