luzhin 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: Torben 13 December 2009 03:48:18PM 2 points [-]

Out of one thousand criminal trials in which the Less Wrong conventional wisdom gave the defendant a 35% chance of being guilty, you would expect to be able to correctly determine guilt nine hundred ninety nine times?

Maybe I'm missing something, but I think you read that wrong.

komponisto said the evidence should not cause anyone to change the prior probability much. Surely, for people in AK's reference class, the per-year probability of committing a 3-party sex killing is less than 0.001?

I think komponisto quite correctly described the effect of privileging the hypothesis, which might be what caused the LW community to be so much off from his estimate. Everybody seemed to be going backward from assuming AK's guilt at 50-50, whereas komponisto went forward from the background probability.

Comment author: luzhin 13 December 2009 09:26:49PM *  0 points [-]

komponisto should not be going forward from the background probabilities because he isn't an experienced investigator with access to the crime scene. he's just a guy reading about evidence on the internet. a more reasonable prior for him to start with is, ''how often are people convicted of murder when they did not in fact commit a murder?'' (there are actual #s for this, too)

when juries sit around thinking, ''is this person guilty or not?'' they assume the investigators working on the case are competent. they assume, quite rightly, that there must be a damn good reason why reasonable investigators couldnt quickly dismiss a hypothesis with such an insanely low prior probability. lesswrong.com readers should do likewise.