Sally
Clark
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 Leeds University.
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 Salford University 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. 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."
