Posts Tagged ‘Bad Statistics Sends woman to Jail’

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7 Conviction By Maths Error

October 20, 2009


sally 3On 9 November 1998 at Chester Crown Court Sally Clark, a Cheshire solicitor, was convicted, by 10-2 majority, of smothering her two baby boys.Clark’s first son died suddenly within a few weeks of his birth in 1996. In 1998, when her second son died in similar circumstances she was arrested and tried for the murder of both sons. The prosecution used paedeatrician Prof Roy Meadows as a expert witness. He had discovered Munchausen Syndrome by Proxy (MSbP) which every student will have seen in some cop show. It relates to an adult, often the mother, inflicting injury or medicating a child to make them sick and to get attention. Sally Clark was found guilty and spent 3 years in jail.

The Maths Error: Not Understanding Statistics!

Prof Roy Meadows testified that the chance of two children from an affluent family suffering sudden infant death syndrome was 1 in 73 million. He arrived at this number by squaring 1 in 8500 for likelihood of a cot death in similar circumstances.

Multiplying the probability of two events only works if the events are independent like flipping a coin. But a Cot Death gene, for instance, would dramatically increase the likelihood of 2 Cot Deaths in one family.

 observer Sally clarkThe Royal Statistical Society later issued a public statement concerning the “misuse of statistics in the courts” and arguing that there was “no statistical basis” for Meadow’s claim. The journalist Geoffrey Wansell called Clark’s experience “one of the great miscarriages of justice in modern British legal history”. Prof Meadows was struck off the medical registrar in 2005. Sally Clark died of acute alcohol poisoning in her home in 2007. (Ref: BMJ )

Article Left: The Observer UK