Stats
The danger of providing expert testimony when you are not an expert (January 31, 2007)
Category: Human side to statistics
Sir Roy Meadow is an expert on child abuse, having published a landmark paper in 1977 on a
condition known as Munchausen Syndrome by Proxy. An observation of his
"one sudden infant death in a family is a tragedy, two is suspicious and three is
murder, unless proven otherwise."
became knows as "Meadow's Law".
In testimony at the trial of a woman, Sally Clark, who had two children who died from
SIDS, Sir Meadow tried to quantify this statement by arguing that the chances of observing
two SIDS deaths would be 73 million to one. He arrived at this figure by squaring the
probability of one SIDS death (8.5 thousand to one). Sally Clark was convicted of murder, but
her conviction was overturned on appeal.
Dr. Meadow's testimony came under criticism, because squaring the probability only makes
sense under independence. If there are genetic or environmental risk factors that influence
SIDS deaths, then the probability estimate could be wrong. Not just wrong, but spectacularly
wrong. It's an error that (hopefully) no statistician would make, but Dr. Meadow is not a
statistician.
The General Medical Council reviewed this case and found Dr. Meadow to be guilty of
serious professional misconduct and erased his name from the medical register. This action,
which would prevent Dr. Meadow from practicing medicine, was still largely symbolic since Dr.
Meadow is currently retired from medical practice.
Dr. Meadows appealed this decision in the British Courts which ruled that the actions of
the General Medical Council should be overturned because expert witnesses will refuse to
testify if they believe that their testimony, if shown later to be invalid, could lead to
sanctions.
There is a wealth of news reports on the original trial and the follow-up. Here are just a
few of the links that I uncovered:
