The danger of providing expert testimony when you are not an expert

Steve Simon


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:

You can find an earlier version of this page on my old website.