Meadow responded in volume , but without defending the statistics he used. Log in to post comments. Vincent, the issue seems to be back in the news.
Are you or David going to update us? Regards, Dave. Hello, i would like to quote you in one of my reports i am writing at the moment on the case of Barry George and what went wrong. I would need to reference this website however and would need to know the year you wrote this article? Thankyou, Mairi. Mairi, the publication date was October I made all these points long ago and I subsequently found out that the RSS had made those points as well.
Why did it never cross their minds to call a statistician to give evidence? Sally Clark might be alive had they done so. I can only assume that it was total ignorance of mathematics and the arrogance to believe that such ignorance is nothing to be ashamed of - almost the opposite.
This is a great analysis of the flaws in the court cases. The trouble with top brains like yourself is that you plunge into calculation without examining the datum. Meadow the mug punter does the same at the races. Unlike most, you observe that it was merely a draft of an intended report and not the report itself. What, then, do you think of its evidential value? The medical argument is much easier to understand than statistics.
There are plenty inherited or partly inherited conditions which can lead to sudden death of a baby. Among these are metabolic diseases, e. MCADD which leads to low blood sugar and cardiac arrest. There must be heart problems e.
If there is even ONE medical explanation that [1] makes cot death of more than one child in a family more likely, [2] is linked to unknown genetic predisposition, and [3] cannot be demonstrated after death [e. In fact, there are MANY such medical conditions. Meadow, a paediatrician, should have known that. Such an important analysis and website. Many thanks. Legal and professional incompetence 1. Evidence was not disclosed to the defence so that appeal was successful.
Flawed statistics 4. Logical Flaws 7. The assumption in this case was that not knowing the cause of cot deaths meant that knowable murder must be the cause 8. Para No 2 there - "The wrong expert Flaws at appeal Search form Search.
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Miscarriages in the British legal sys Aboriginality in Sally Morgan's M Far more children die of natural causes in general than specifically of cot death. The Campaign to free Sally Clark claim that around fifty families every year in the UK have a second child die naturally. Of course, in many of these cases the cause of death will be very clear, so this figure is not terribly relevant to Sally Clark's case either, but it does lend further weight to the statement that Sally Clark had no real case to answer.
One of the problems with statistics is that there are so many. Often, such a large number of factors could influence a probability calculation that the choice of which to take into account must be made with the greatest of care in order to avoid charges of bias. Nobody is suggesting that the prosecution was unscrupulous, but they did have a case to make - after all, that is what a prosecution does.
And the statistic that they chose to use took into account all the factors that made cot death less likely in Sally Clark's case and ignored those that made it more likely. For example, both Sally Clark's children were boys. Boys are more likely than girls to die of cot death nearly two thirds of cot deaths are boys. Far more importantly, if they wanted to take into account the factors that made cot death less likely in a family like the Clarks, they should also have taken into account the factors making murder less likely in such a family.
Home Office figures suggest fewer than 30 mothers a year kill their own child. And in most of these cases the children have been poorly cared for, Social Services have had files on the family, the family is poor, only one parent is on the scene, and so on.
No such factor was present in this case. In other words, just as the Clarks were atypical for cot death, they were also atypical for murder - but this fact was completely ignored in the prosecution's single statistic. All these arguments pale into insignificance compared to the final charge that the statistic was totally misleading.
There is good reason to believe that the jury completely misunderstood it. Very possibly, as you're reading this, you are making the same mistake. Are you thinking "okay, so the odds aren't as extreme as 1 in 73 million, but they're still astronomically high.
There's not that much difference between odds of 1 in 73 million and 1 in ,, so Sally Clark must still be guilty. Simply put, this is the incorrect belief that the chance of a rare event happening is the same as the chance that the defendant is innocent. Even with the more accurate figure of 1 in , for the chance that a randomly chosen pair of siblings will both die of cot death, this is not the chance that Sally Clark is innocent.
It is the chance that an arbitrary family will lose two children in cot deaths. It's not the most scary statistic you will ever read, but in a big country like England, even such improbable events will happen often enough.
Are we to believe, with no evidence, that every mother bereaved in this way is a murderer, just because such an event will only happen a few times a year?
So how should you assess the likelihood, in the absence of any reliable forensic evidence, that Sally Clark murdered her two little boys? The tool you need is called Bayes Theorem, and it allows you to combine the probabilities of various events to weigh up their respective relative likelihoods. In nonmathematical language, Bayes Theorem allows you to separate how likely alternative explanations of an event are, from how likely it was that the event should have happened in the first place.
In Sally Clark's very rare predicament, practically all the improbability is taken up by the fact that two of her children died at all. In the rich world, most children born alive stay alive. So although every possible explanation for their deaths is highly unlikely, this is just because their deaths were unlikely in the first place. But something caused them to die, and to avoid the Prosecutor's Fallacy, the proper thing to do is to decide which explanations are relatively most likely.
In mathematical language, we need to find the conditional probabilities of the various possible causes of death, given the fact that the children died. Sally Clark was arrested after her second baby died a few months old, apparently of sudden infant death syndrome SIDS , exactly as her first child had died a year earlier. They argued that there is only a probability of that two such deaths would happen in the same family by chance alone after controlling for tobacco smoke and a few social factors.
According to the prosecution, the woman was guilty beyond a reasonable doubt. The jury returned a guilty verdict, even though there was no substantial evidence of guilt presented beyond this argument. Note that the latter two are meant to establish the appearance of SIDS deaths.
Then the prosecutor's argument was:. There are a lot of problems with this argument. Here I will discuss the two most basic errors, which probably have the most impact and which anyone involved with assessing evidence should be capable of recognizing. First, the combination of the evidence in 2 , simply by multiplication, requires the two pieces of evidence to be independent of each other.
The general form of such a combination is , which further reduces to 2 only if , that is, only if the two items of evidence are independent given innocence.
However, risk factors for SIDS are very likely to be common to multiple children within a family, including not the just tobacco smoke and the social factors controlled for, but also poor prenatal care, low birth weights, alcohol consumption and sleeping practices and, to be sure, physical abuse by parents. One study reported a relative risk of recurrence of SIDS of 5 times the background rate, a rate found to be comparable to other recurrent mortality risks in siblings.
This yields , instead of. The second failure in the prosecution argument is the complete neglect of prior probabilities. Bayes' rule says:. Contrary to a widespread view in the legal community that statistical, and especially Bayesian, reasoning should not be considered in court proceedings, it is crucial in many cases that such reasoning be used — but, of course, used correctly.
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