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dilaudid comments on The Amanda Knox Test: How an Hour on the Internet Beats a Year in the Courtroom - Less Wrong

42 Post author: komponisto 13 December 2009 04:16AM

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Comment author: dilaudid 13 December 2009 05:23:15PM 23 points [-]

Komponisto makes a strange assertion. The prior is not the reference that "someone would commit murder" - there is a body. A more appropriate prior is "someone who lives with someone who was murdered committed that murder" - I'm guessing that base probability is of the order of 0.1. Once we take into account that AK and MK aren't in a relationship, AK is female, and there is very strong evidence that someone else committed the murder then I'd agree that the probability drops, but these pieces of evidence don't cancel out leaving us with the original prior - the final probability may be higher or lower.

Also the "complexity penalty on the prosecution's theory of the crime is enormous" - that may mean the case was flawed, but it's not evidence she didn't kill MK unless you are willing to give some weight to the conviction (at <0.001, I assume you are not). Or to put it another way, even if the prosecution is completely wrong you cannot set the probability of guilt to 0. This is like assuming AK is guilty because her parents criticized the Italian legal system.

Overall I hope I am a bit more cautious about my abilities than you. In the first half you explain why you, as a human being, cannot be trusted to be rational. Then you set out your case. Why should I trust your rationality, but not others'?

Comment author: brazil84 14 December 2009 03:48:16AM 3 points [-]

I think this is a good point, but I would go one step further. Because there was more than one crime committed. In addition to a murder, somebody tried to stage a burglary. Common sense says that whoever staged the burglary was also involved in the murder but it's still 2 separate crimes.

It seems to me that the prior probability that the person who staged the burglary is someone closely associated with Kercher, such as a roommate, is actually pretty high. A close associate would have a strong incentive to try to make the police think that a stranger committed the crime. Whereas a stranger or remote acquaintance would have little or no incentive to do so.