Christian Long

Peter Donnelly: How Stats Fool Juries

In TED Talks on April 12, 2010 at 9:58 am

Reflection by COLTON C.

Original TED page w/ speaker bio, links, comments, etc:

Peter Donnelly:  How Stats Fool Juries

Peter Donnelly is a great statistician who is a professor at Oxford.

He gives many examples of how even the smartest mathematicians get the simplest probability problems wrong. All of his examples are leading up to his final point about a woman who lost both of her children at birth. In his first example with coins, he asks which pattern will normally come first, HTH( head, tails, head) or HTT( head, tails, tails). The average person will say they both have the same probability of happening but that is wrong and he explains why.

Then Peter explains his real love is for genetics. He talks a little about the human genome project and how it fits in with diseases and natural defects. This later ties into his point about the court case.

The first assumption of what happened to Sully Clark’s babies is that they died of cot death, or sudden infant death syndrome. Later for some reasons she was accused of killing her two babies. Her family was a professional, non smoking family. A distinguished pediatrician said at the trial that the chances of both kids dying were 1 in 73 million. Due to those numbers, the woman was convicted and sent to jail. After the second appeal, she was finally cleared of the accusations.

What the pediatrician did not take into account is that there is not much knowledge on cot deaths. Also the court did not take into account that this was just an assumption and they did not even check to see if it was true. Another things is that he was a pediatrician, not a mathematician or a statistician who would have been able to find the real probability of the babies dying.

The last thing Mr. Donnelly wants to point out is that when it comes to reasoning with uncertainty, you are wrong every time.


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