George Claassen

Science under scrutiny in court

2005-07-29 09:22

The news two weeks ago that Sir Roy Meadow, one of the most prominent paediatricians in the United Kingdom, was struck off the medical register for giving erroneous and misleading evidence that helped to send a mother to a life sentence in jail, has serious consequences for the legal and science professions.

The UK's General Medical Council ruled that Meadow, although not intentionally, was guilty of serious professional misconduct because he misled the jury in the trial of Sally Clark, who was found guilty of the murder of her two sons who died of cot death.

Clark's release in 2003 after spending two years in jail, was mainly because numerous other scientists doubted the expertise of Meadow's testimony.

The British Mathematical Society questioned the way in which the jury was swayed by the erroneous statistics used by Meadow in his expert testimony for the prosecution.

Meadow's testimony also led to the wrongful conviction of Angela Cannings and Donna Anthony, who were also vindicated like Clark.

Meadow's testimony in numerous cot death cases became known as Meadow's Law: "One sudden infant death is a tragedy, two is suspicious and three is murder, unless proven otherwise."

According to a former president of the Royal Statistical Society, Prof Peter Green, Meadow's Law did not take mathematical statistics into account.

He said that the convicted mothers were victims of what he called "Prosecutor's Fallacy", a tendency in the legal profession according to which prosecutors wrongly interpret statistics and sway juries to make wrongful convictions because of erroneous mathematics.

The president of the British Mathematical Society in 2002-2003, Prof Barry Lewis, asked in his presidential address in 2003 what lessons Sally Clark's trial could teach all about mathematics.

'We have a big problem'

It tells us that we have a big problem, a problem not only that some people fail mathematics, but also that people who pass successfully in other subjects, often don't grasp anything about mathematics, Lewis said.

If QCs, judges, and even well-known scientists do not grasp simple statistics, what chance do the rest of the population have?

Lewis said we should understand the paradox: while the world becomes more mathematical, mathematical literacy becomes even more rare.

What swayed the heads of the jury in the case of Sally Clark, who was a lawyer in Cheshire, England when her two sons died, was Meadow's 1 out of 73 million chance statistics that two babies within an affluent family could both suffer cot deaths.

Referring to these erroneous statistics Lewis said the real statistics, according to the calculation model of Bayes, also known as the Theorem of Bayes, showed that the possibility that the cot deaths were normal, stood at 0.625.

This means that the chances that Clark was innocent, was bigger than 1 in 2, which was a very long way from the 1 in 73 million statistics proposed by Meadow.

What are the implications of the Meadow sanctioning and the successful appeals of Clark and other wrongfully convicted mothers?

Scientific 'experts'

Both for the science and legal professions it means the scientific "experts" called to testify, should really be experts in their field.

The chairperson of the British panel who found Meadow guilty, Mary Clark-Glass, warned Meadow that he had failed in his duty by straying outside his area of expertise.

In 2002 the National Academies of Science and the US legal profession came together to discuss the problem of credible scientific testimony in court cases and to find improved mechanisms to ensure that expert testimony is indeed that.

Four guidelines according to which expert scientific testimony and evidence can be judged, were set by the US Supreme Court in Daubert v Merrell Dow Pharmaceuticals in 1993.

The emphasis was that the court should play a gatekeeping role in this regard: Were the theories or techniques on which the testimony of an expert was based, rooted in testable scientific claims? (Double-blind testing is for example often absent from so-called experts' testimony.)

Was the theory or technique peer reviewed? (Many experts base their testimony on their own personal view of a case, without taking the scientific system of peer review into consideration.)

Is there a definite or potential mistake possibility that can be related to the scientific method?

Is the method accepted by the relevant scientific community? (In Meadow's case the mathematical experts clearly did not agree with him.)

Judge's need to be 'evidentiary gatekeepers'

Speaking in February 1998 before the American Association for the Advancement of Science, Justice Stephen Breyer emphasised that the law imposes upon trial judges the duty, in respect to scientific evidence, to become evidentiary gatekeepers.

The judge, without interfering with the jury's role as trier of fact, must determine whether purported scientific evidence is 'reliable' and will 'assist the trier of fact,' thereby keeping from juries testimony that is wrong.

Trial judges, looking for ways better to perform this function, increasingly have used pre-trial conferences to narrow the scientific issues in dispute, pre-trial hearings where potential experts are subject to examination by the court, and the appointment of specially trained law clerks or what Breyer called scientific "special masters".

Send your comments to George or discuss this column now in our debating forum.

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  • George Claassen is science editor of Die Burger, Cape Town's largest circulation daily newspaper.


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