Sunday, July 24, 2011

Rules of Evidence

Sometimes people need to learn the rules of conditional probability.

A story that I read went as following (not 100% sure if this is true but seems to kind of line up with the evidence).

"In the famous murder trial, OJ Simpson matched a blood test that 1 out of 1,000,000 people match. Johnny Cochrane's defense was along the lines of "There are six men walking around LA who could have killed Nicole Brown."

Yes, but the chance that OJ is guilty given that he matched the blood test AND she is his ex-wife is way better than 1 in 6.

Cut to today and Amy Winehouse's death.

Police said the cause of her death is being treated as "unexplained," rejecting speculation that she died from a drug overdose as "inappropriate."

Of 27 year old women who die suddenly and unexplainedly, I'm not sure what the proportion of "drug overdose" is. I'm going to guess one out of 20 or so -- heart attacks and strokes aren't terribly common in this age demographic.

But given that Winehouse used heroin, cocaine, ecstasy, and alcohol, at the same time....the probability that Amy Winehouse died of a drug overdose is a lot higher that one in 20.

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