March 25, 2012

In 1999 Solicitor and mother, Sally Clark was convicted of murdering her two children. The Statition allocated to the prosecution presented the jury with outrageously miscalculated statistics. Because of this, Clark was sentenced to TWO life sentences. Her story has since been published as a book by John Batt and is truly heart-rending.

Clarks first child Christopher, died three years prior to the ’99 trial, at age 3 months. His death had originally been treated as arising due to natural causes, some said “Sudden Infant Death Syndrome” otherwise known as SIDS.  When her second child, Harry, died a year later age two months the Home Office pathologist who carried out the post-mortem determined that both deaths were suspicious. Sally Clark was arrested and tried at Chester Crown Court.

During the trial, statistical evidences was given by one of the prosecution witnesses, Professor Sir Roy Meadow. Meadow was a highly respected expert in field of child abuse and the author of  leading textbook ‘The ABC of Child Abuse’. His evidence was outrageously flawed, through miscalculations Meadow concluded that neither child had dies of natural causes and in fact, the likely hood of this was actually 1 in 73 million. Suggesting to the jury that there was a 1 in 73 million chance that she was innocent, falling foul of ‘prosecutors fallacy’  (’s_fallacy). The medical evidence for this statistic provided by the Professor was extremely complicated. I believe the jury cannot be blamed for adopting the belief because surely we should have every faith in a man such as this.

How could he possibly have come to this conclusion ? Where are the mistakes? …..

one crucial piece of Meadows evidence was not of a medical nature at all, but instead was based on a report that he was involved with. At the time of the trial, the Professor was writing a preface to a report of a government funded research team, the ‘Confidential Enquiry into Sudden Death in Infancy’ or ‘CESDI’. The report covered an in depth study of over 400 sudden infant deaths in the UK over a 3 year period. Its aim was to establish possible risk factors for sudden or unexpected deaths in infants. These factors included the mothers ages, whether any parents were smokers and whether the household included a wage-earner. The Clark household had none of the forementioned risk factors. Therefore Meadow concluded from the CESDI study that the chance of SIDS in this case was 1 in 8,543 and is quoted as saying : ““you have to multiply 1 in 8,543 times by 1 in 8,543 and I think it gives that in the penultimate paragraph, its (sic) points out that it’s approximately a chance of 1 in 73 million”. Basically, he calculated each death independently of eachother using a similar method as we would for guessing the probability of rolling a 6 on a dice immediately after already rolling a 6. He even used a Grand National analogy that you can find here (as it’s rather lengthy, i can only assume this was in order to confuse the jury further) (Page 164)

Some weeks later the British Medical Journal published an article suggesting that SIDS was not a random event and that double SIDS may even occur every 18 months, not every 100 years as suggested by Prof. Meadow. Surely, whether you are an expert or an outsider – would it not cross your mind that SIDS may be hereditary?

Unfortunately this is not the only case in which the misuse of statistics has led to very unjustified and saddening endings. And unsurprisingly  when Radio 5 live and The Observer paper put a number of questions to the Professor concerning Clark he declined to talk to them for danger of “being sticthed up” – to be quite honest, this really sickens me. We should be able to have faith in experts such as Meadow to provide us with truthful statistics, not those twisted to meet his needs. Especially in circumstances such as these where a mother lost her two boys and was convicted of their murder.

… and very sadly, it led to this:

I found the story genuinely upsetting, so i hope i haven’t caused any distress to anyone whose chosen to read this. I hope that instead it encourages you to think more carefully about how you present your own research and think about how honest you’re being in disclosing them.



  1. fr4nw Says:

    I think that this is a very unfortunate incident and I think we all hope never to be in such a situation where our research condemns an innocent person. When you mentioned how you believe that the jury are not to blame for believing the statistician it reminded me of the debate concerning whether research should be written for the researcher or for the layman. This is because although usually in this debate we think about journals and maybe even the limited view provided by the media it is also applicable to situations such as providing the jury with information that has some bearing on the evidence. O’Grady (2007) supports this point with research into the role of a psychiatrist in court stating that the psychiatrist being confident in their abilities, knowing their limitations and the importance of conveying clear information to enable the court to fully understand any psychiatric conditions presented in the court case. Therefore to some extent I feel that it is possible that this incident could have been avoided if the jury were able to comprehend the work of the statistician, as understanding could have given the jury the opportunity to question his work.
    O’Grady, J.C. (2007). Report writing for the criminal court. Psychiatry, 6(11), 462 -464. Retrieved from:

  2. psucd8 Says:

    I found this story really sad that the mistake of one person can lead to such devastating consequences. A video I have found on youtube demonstrates some examples as to how it can be easy to get confused by stats and make a mistake, and that often professional mathematicians often can get things wrong. It also demonstrates how this can happen when looking at the genetic basis of diseases, and how people can come to incorrect conclusions if they do not take the context of the stats into account. An example describes how a test can be 99% accurate in diagnosis, so if a person at random is selected and shown to have a particular illness it does not mean that the probability the person has the illness is 99% as it is not taken in context. When accompanied by the knowledge of the ratio of how many people are affected, sometimes the percentage of people falsely diagnosed will be higher than those accurately diagnosed as having the illness. He goes on to relate this example to the situation you described (14mins onwards) and how the statistician used the incorrect assumption like above to suggest that the likelihood of the event occurring was 1 in 73million

    In the case of Sally Clark although the statistician had used the assumption that the two deaths were independent of each other this was not stated to the Jury, therefore the statistics were not given in sufficient context for the Jury to understand what this meant and what the potential flaws in the calculation were. It does not allow them to analyse the data efficiently to realise that this statistic is not taking into account the genes and environment that the two children shared that may increase their risk of SIDS. The way the information was presented to the jury saying that there was a 1 in 73million chance that Sally Clark was innocent was also wrong as it does not take into account the other evidence that may indicate that she was not guilty. I think this example is really important to demonstrate how stats can easily be miscalculated if context is not taken into account, and how this can have devastating effects.


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  4. ksarah20 Says:

    I agree that it’s an awful thing for anyone to go through being wrongly convicted of a crime they didn’t commit. Unfortunately in life these things can happen though. It’s not just statistics that can lead to a false conviction; false memories have caused some people to be convicted of crimes they didn’t comment. Loftus has written a very interesting article on the law and the implications of false memory and convictions,

  5. psuc15 Says:

    You have taken a truly emotional and powerful example of the impact statistics can have on individuals as well as their circumstance identifying the tragic outcomes that can arise from such situations. This brings to light the discussion of the level of trust we bestow into the professional figures and how influential their opinions and comments can be perceived.
    You have taken a mature approach to such a sensitive topic as well as addressing the nature of the blog to your audience taking their feelings into consideration for those who read the information. With such an extreme example it is difficult to focus on the other side of the story in that not all professionals manipulate their position and display controversial figures. From a different point of view each person had their own choice to make within this case either choosing to take on face value the information that was presented or to question it unfortunately authority roles cloud this judgement often leading people to believe that they don’t have the right to question information presented to them which is not the case.
    All in all a powerful blog with a clear message well done on maintaining a mature approach to this case.

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