Difference between revisions of "I was quoting the statistics, I wasn't pretending to be a statisitcian"

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There are two obvious problems with this 1 in 73 million statistic: (1) Because of environmental and genetics effects it seems very unlikely that the a SIDS death for a families the first baby and for their second baby are independent and (2) Giving these odds  might suggest to the jury that there is a 1 in 74 million chance that Sally Clark is innocent. If not, why were they  given? Ålso medical experts testimony was very technical and the some of the experts opions were contradictory so the odds were something they could understand. Of couse these odds are useless unless we know the corresponding odds that the deaths are the result of murders.  In his article on the Sally Clark trial Professor Roy Hill estimated, that for a randomly chosen family  with two baby deaths, the probabillity that the deaths are the result of SIDS is about 10 times more likely than that it is the result of murders.  This if this kind of statitical evidence means anything, given no other information,  it suggests that Sally Clark is innocent.  
 
There are two obvious problems with this 1 in 73 million statistic: (1) Because of environmental and genetics effects it seems very unlikely that the a SIDS death for a families the first baby and for their second baby are independent and (2) Giving these odds  might suggest to the jury that there is a 1 in 74 million chance that Sally Clark is innocent. If not, why were they  given? Ålso medical experts testimony was very technical and the some of the experts opions were contradictory so the odds were something they could understand. Of couse these odds are useless unless we know the corresponding odds that the deaths are the result of murders.  In his article on the Sally Clark trial Professor Roy Hill estimated, that for a randomly chosen family  with two baby deaths, the probabillity that the deaths are the result of SIDS is about 10 times more likely than that it is the result of murders.  This if this kind of statitical evidence means anything, given no other information,  it suggests that Sally Clark is innocent.  
  
As far as we can tell only problem (1) was seriously discussed in the news.  The first news article we could find  discuss this issue appears to be  "False statistics may have led to solicitor's murder conviction" by Sherry Norton in The Independent (London), December 31, 1999. This article reports on and article by Dr Stephen Watkins, director of public health at Stockport health entitled "Conviction by mathematical error? (BMJ, 2000, 320, 2-3).  Norton writes:
 
  
  

Revision as of 18:33, 27 July 2005

Sir Roy Meadow struck off by GMC
BBC News, 15 July 2005

Beyond reasonable doubt
Plus Magazine, 2002
Helen Joyce

Multiple sudden infant deaths--coincidence or beyond coincidence
Paediatric and Perinatal Epidemiology 2004, 18, 320-326
Roy Hill

___________________________________________________________________________________

Sir Roy Meadow is a pediatrician well known for his research in child abuse. The BBC article reports that the UK General Medical Council (GMC) has found Sir Roy guilty of serious professional misconduct has "struck him off" the medical registry. If upheld under appeal, this will prevent Meadow from practicing medicine in the UK.

This decision was based on flawed statistical estimate that Meadow made while testifying as an expert witness in a 1999 trial in which a Sally Clark was found guilty of murdering her two baby boys and given a life sentence.

To understand his testimony we need to know what a SIDS (sudden infant death syndrome) is.

The name SIDS was proposed by the pathologist Bruce Beckwih at a conference in 1969 and the definition, which is still current, was formulated at the conference by Beckwith and others as follows:

The sudden death of a baby that is unexpected by history and in whom a
thorough post-mortem examination fails to demonstrate an adequate cause of death.

The death of Sally Clark's first baby was reported as a cot death which is another name for SIDS. Then when her second baby died she was accused of murdering both her children.

We were not able to find a transcript for the original trial but we were able from Lexis Nexis (1) to find transcripts of two appeals that the Clarks made, one in October 2000 that they lost, and the other in 2003 which they won and Sally Clark was released from jail. The 2003 transcript reported on the statistical testimony in the original trial as follows:

Professor Meadow was asked about some statistical information as to the happening of two cot deaths within the

same family, which at that time was about to be published in a report of a government funded multi--disciplinary research team, the Confidential Enquiry into Sudden Death in Infancy (CESDI) entitled 'Sudden Unexpected Deaths in Infancy' to which the professor was then writing a Preface. Professor Meadow said that it was 'the most reliable study and easily the largest and in that sense the latest and the best' ever done in this country.

It was explained to the jury that there were factors that were suggested as relevant to the chances of a SIDS death within a given family; namely the age of the mother, whether there was a smoker in the houshold and the absence of a wage-earner in the family.

None of these factors had relevance to the Clark family and Professor Meadow was asked if a figure of 1 in 8,543 reflected the risk of there being a single SIDS within such a family. He agreed that it was. A table from the CESDI report was placed before the jury. He was then asked if the report calculated the risk of two infants dying of SIDS in that family by chance. His reply was: 'Yes, you have to multiply 1 in 8,543 times 1 in 8,543 and I think it gives that in the penultimate paragraph. It points out that it's approximately a chance of 1 in 73 million.'

It seems that at this point Professor Meadow's voice was dropping and so the figure was repeated and then Professor Meadow added: 'In England, Wales and Scotland there are about say 700,000 live births a year, so it is saying by chance that happening will occur about once every hundred years.'

Mr Spencer [for the prosecusion] then pointed to the suspicious features alleged by the Crown in this present case and asked: 'So is this right, not only would the chance be 1 in 73 million but in addition in these two deaths there are features which would be regarded as suspicious in any event?' He elicited the reply 'I believe so'.

All of this evidence was given without objection from the defence but Mr Bevan QC (who represented the appellant at trial and at the first appeal but not before us) cross--examined the doctor. He put to him figures from other research that suggested that the figure of 1 in 8,543 for a single cot death might be much too high. He then dealt with the chance of two cot deaths and Professor Meadow responded: 'This is why you take what's happened to all the children into account, and that is why you end up saying the chance of the children dying naturally in these circumstances is very, very long odds indeed one in 73 million.' He then added:

'. . . it's the chance of backing that long odds outsider at the Grand National, you know; let's say it's a 80 to 1 chance, you back the winner last year, then the next year there's another horse at 80 to 1 and it is still 80 to 1 and you back it again and it wins. Now here we're in a situation that, you know, to get to these odds of 73 million you've got to back that 1 in 80 chance four years running, so yes, you might be very, very lucky because each time it's just been a 1 in 80 chance and you know, you've happened to have won it, but the chance of it happening four years running we all know is extraordinarily unlikely. So it's the same with these deaths. You have to say two unlikely events have happened and together it's very, very, very unlikely.'

The trial judge clearly tried to divert the jury away from reliance on this statistical evidence. He said: 'I should, I think, members of the jury just sound a word of caution about the statistics. However compelling you may find them to be, we do not convict people in these courts on statistics. It would be a terrible day if that were so. If there is one SIDS death in a family, it does not mean that there cannot be another one in the same family.'

Note that Meadow obtained the odds of 73 million to one from the CESDI report so there is some truth to the statement "I was quoting the statistics, I wan't pretending to be a statisician" that Meadow made to the General Medical Council. Note also that both Meadow and the Judge took this statistic seriously and must have felt that it was evidence that Sally Clark was guilty. This was also true of the press. The Sunday Mail (Queenstand, Australia) in an article titled "Mum killed her babies" we read

Medical experts gave damning evidence that the odds of both children dying from cot death were 73 million to one.

There are two obvious problems with this 1 in 73 million statistic: (1) Because of environmental and genetics effects it seems very unlikely that the a SIDS death for a families the first baby and for their second baby are independent and (2) Giving these odds might suggest to the jury that there is a 1 in 74 million chance that Sally Clark is innocent. If not, why were they given? Ålso medical experts testimony was very technical and the some of the experts opions were contradictory so the odds were something they could understand. Of couse these odds are useless unless we know the corresponding odds that the deaths are the result of murders. In his article on the Sally Clark trial Professor Roy Hill estimated, that for a randomly chosen family with two baby deaths, the probabillity that the deaths are the result of SIDS is about 10 times more likely than that it is the result of murders. This if this kind of statitical evidence means anything, given no other information, it suggests that Sally Clark is innocent.



References

Transcriipt for the 2000 and 2003 appeals can be obtained from Lexis Nexis following the following route:

Open Lexis Nexis

Choose "Legal Research" from the sidebar

From "Case Law" choose "Get a Case"

Choose" Commonwealth and Foreign Nations" from the sidebar

Choose "Sally Clark" for the " Keyword"

Choose "UK Cases" for the "Source"

Choose "Previous five years" for the "Date."

The two " r v Clarks" are the appeals.

To be continued