Class, 11/12

We discussed the Wuppertal, Germany case discussed in Calculated Risks, pp. 156-158. Our take on discussing the probability tree started with a 1 chance in 100000 that the person arrested was guilty, since there are about that many people in the area and with no data, the prior has to depend only on general information like this. So the probability of innocence in for all practical purposes equal to 1.

We then decided that there was an 8 in 10 chance that there would be blood on the shoes, given guilt, but only a 1 in 1000 chance, given innocence.

We further used the 2.7% match probability, given innocence, that was mentioned in the book, and a match probability of 1, given guilt.

All of this data still did not make the probability up to the 99% probability of guilt that we discussed in earlier classes.

I then pointed out that the suspect turns out to have had an ironclad alibi. He was 100 km away at the time of the murders.

We started discussing the O. J. Simpson case. We'll look at it in more detail next time.