Meadow's law
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Meadow's Law was a precept much in use until recently in the field of child protection, specifically by those investigating cases of multiple cot or crib death — SIDS — within a single family.
The 'law' has it that because such deaths are a rare phenomenon and difficult to explain by natural causes, we might say that "One is a tragedy, two is suspicious and three is murder unless there is proof to the contrary."
The name is derived from the controversial British paediatrician, Roy Meadow, who until recently was seen by many as his country's leading expert on child abuse. Meadow's reputation went into decline from 2003 with a series of legal reverses for his theories, and the damage was confirmed in July 2005 when he was struck off the medical register by the General Medical Council (for tendering misleading evidence). Meadow's license was reinstated in February 2006 by a London court.
Meadow attributes many unexplained infant deaths to the disorder or condition in mothers that he calls 'Munchausen Syndrome by Proxy'. According to this 'diagnosis' some mothers harm or even kill their children as a means of calling attention to themselves.
As a result of the Allitt trial in 1993, 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 both of Munchausen's and 'Meadow's Law'. Several convictions were reversed, and many more came under review.
The only source in the British literature for ‘Meadow’s Law’ is Meadow’s ABC of Child Abuse, the first edition of which appeared in 1989. That was the year the precept was set down in print in the United States by DiMaio and DiMaio, without mention of Meadow. If he borrowed the term from them he makes no acknowledgement. Some have said that we ought properly to speak of ‘the DiMaios’ Law’:
“There have been a small number of reports of more than one SIDS death in a family and of SIDS death in twins. Some of these cases are probably due to random chance. The majority of them, however, probably represent infanticide. It is the general policy of the authors to ascribe the first death in a family presenting as SIDS to SIDS. The second death by the same mother is labeled as undetermined and a more intensive investigation of the circumstances surrounding the death is conducted. … A third such death in the family is felt by the authors to be homicide until proven otherwise.”
(Dominic J. DiMaio and Vincent J.M. DiMaio, Forensic Pathology, Elsevier, St. Louis MO, 1989, p. 291)
The formula is “clearly fallacious” according to Bob Carpenter, Professor of Medical Statistics at the London School of Hygiene and Tropical Medicine (quoted at abc.net.au, in a posting of 24 January 2005).
The ‘law’ seems in Britain to have been adopted literally and urged by police and childcare workers — individuals with no training in paediatrics — who have acquired the habit of deferring to medical opinion as the immutable foundation for their actions, even though they don't fully understand what that opinion is. It appears that some child protection workers have applied the Meadow hypothesis as dogma, without its ever having been formally elaborated or defended. Another fact is that the prosecutions in which Meadow’s views played a role were often covered for the popular press by hardbitten crime reporters rather than by thoughtful journalists, and this may have had some effect in establishing the precept.
[edit] Criticisms of Meadow's law
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 (approximately 8,500:1).
This caused an uproar amongst professional statisticians, whose criticisms were twofold:
[edit] The prosecutor's fallacy
Firstly, Meadow was accused of espousing the so-called prosecutor's fallacy in which the probability of "cause given effect" (i.e. the true likelihood of a suspect's innocence) is confused with that of "effect given cause" (the likelihood that innocence will result in the observed double-cot-death). In reality, these quantities can only be equated when the likelihood of the alternate hypothesis, in this case murder, is close to certainty. Since murder (and especially double murder) is itself a rare event, the probability of Clark's innocence was certainly far greater than Meadow's figure suggested.
[edit] 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 (such as a hypothesised "cot death gene") 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 (estimates are mostly in the region of 1:100).
Some mathematicians have estimated that taking both these factors into account, the true odds may have been in the region of 2:1 in favour of Clark's innocence, a far cry from Meadow's 1:73,000,000 against.
