Meadow's law

Meadow's Law is a now-discredited legal concept once used to adjudicate cases involving multiple instances of sudden infant death syndrome, also known as crib or cot deaths, linked to a single caregiver. Due to the rarity and often inexplicable nature of these deaths, the law posited that "one ''sudden infant death is a tragedy, two is suspicious and three is murder until proved otherwise."'' Now recognized as fundamentally flawed and based on misunderstanding of statistics, Meadow's Law has been heavily criticized for leading to wrongful convictions and accusations.

History

The name is derived from the controversial British paediatrician Roy Meadow, who until 2003 was seen by many as "Britain's most eminent paediatrician" and leading expert on child abuse. Meadow's reputation went into decline with a series of legal reverses for his theories, and in July 2005 he was struck off the medical register by the General Medical Council for tendering misleading evidence. Meadow's licence was reinstated in February 2006 by a London court.
Meadow attributes many unexplained infant deaths to the disorder or condition in mothers called Munchausen syndrome by proxy. According to this diagnosis some parents, especially mothers, harm or even kill their children as a means of calling attention to themselves. Its existence has been confirmed by cases where parents have been caught on video surveillance actively harming their children, but its frequency is subject to debate as Meadow claimed to have destroyed the original data which he used to substantiate the law.
As a result of the 1993 trial of Beverley Allitt, a paediatric nurse convicted of killing four children under her care and injuring five others, Meadow's ideas gained ascendancy in British child protection circles, and mothers were convicted of murder on the basis of his expert testimony. Thousands of children were removed from their parents and taken into care or fostered out because they were deemed to be 'at risk'. From 2003, however, the tide of opinion turned: a number of high-profile acquittals cast doubt on the validity of 'Meadow's Law'. Several convictions were reversed, and many more came under review.

Attribution to the Di Maios

In a note to his mathematical analysis of the Sally Clark case, Professor Ray Hill endorses a claim that Meadow did not originate the rule:
The precept was published in the United States by DiMaio and DiMaio in 1989, without mention of Meadow. It is often claimed, quite falsely, that in ABC of Child Abuse, first published in the same year, Meadow wrote his formulation:
. There is no such passage in that book.
The formula is "clearly fallacious" according to Bob Carpenter, Professor of Medical Statistics at the London School of Hygiene and Tropical Medicine, an expert witness in some of the trials where infant cot deaths were prosecuted as homicides.

Criticisms

Critics of Meadow's law state that it is based on a fundamental misunderstanding of statistics, particularly relating to probability, likelihood, and statistical independence.
At the trial in 1999 of solicitor Sally Clark, accused of murdering her two sons, Meadow testified that the odds against two such deaths happening naturally was 73,000,000:1, a figure which he obtained by squaring the observed ratio of births to cot-deaths in affluent non-smoking families.
This caused an uproar among professional statisticians, whose criticisms were twofold:

The prosecutor's fallacy

Firstly, Meadow was accused of espousing the so-called prosecutor's fallacy in which the probability of "cause given effect" is confused with that of "effect given cause". In reality, these quantities can only be equated when the likelihood of the alternative hypothesis, in this case murder, is close to certainty. Since murder is itself a rare event, the probability of Clark's innocence was certainly far greater than Meadow's figure suggested.
An equivalent error is to accuse anybody who wins a lottery of fraud.

Statistical independence

The second criticism was that Meadow's calculation had assumed that cot deaths within a single family were statistically independent events, governed by a probability common to the entire affluent non-smoking population. No account had been taken of conditions specific to individual families which might make some more vulnerable than others. The occurrence of one cot-death makes it likely that such conditions exist, and the probability of subsequent deaths is therefore greater than the group average.
Combining these corrections with estimates of successive murder probabilities by affluent non-smokers, Mathematics Professor Ray Hill found that the probability of Clark's guilt could be as low as 10%. In any case, a legal verdict is not to be rendered on the basis of statistics; Hill wrote, "guilt must be proved on the basis of forensic and other evidence and not on the basis of these statistics alone. My own personal view that she is innocent is based on my subjective assessment of all the aspects".