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

42 13 December 2009 04:16AM

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Comment author: 13 December 2009 06:54:17AM 8 points [-]

@OP: you have appealed to rationality in examining this case... then you come up with this:

"1. Negligible. No different from the prior, which is dominated by the probability that someone in whatever reference class you would have put Amanda into on January 1, 2007 would commit murder within twelve months. Something on the order of 0.001 at most. "

The FACTS include 1) the police came to "her house" and discovered a murder victim in one bedroom and 2) she was tried and convicted. You seem to have given these zero weighting in your final calculation.

And this:

"3. About as high as the other two numbers are low. 0.999 as a (probably weak) lower bound."

Did your prior of "0.001 at most" apply to Guede as well?

I offer \$50 to the AK defense fund if you can produce a defensible Bayesian probabilities calculation showing how you got from your priors to your final probabilities. A condition is that you must account for the fact that most (let us say 80% for the purposes of your calculation) persons convicted of a crime in a democratic society are in fact guilty of it, and that you use generally defensible assumptions.

Should you try to do so, Less Wrong readers can decide if you have succeeded by voting on the post containing your calculation.

D. Alex

Comment author: [deleted] 13 December 2009 07:30:18AM 4 points [-]

While I have a sort of vague sense of disagreement with this comment, I voted it up, because I would be very interested in an example of Bayesian reasoning applied to the real world without having a truckload of given probabilities to work with. In particular, I don't know how one would take into account D_Alex's 80% while also taking into account more specific factors.

Comment author: 13 December 2009 05:13:11PM 5 points [-]

I had the same reaction. I'm strongly inclined toward the OP's position, but if you're going to excoriate everyone else for failing to "jettison [their] intuitive feelings in favor of cold, hard, abstract calculation", you should provide the actual cold, hard, abstract calculations supporting your own position.

Comment author: 18 December 2009 08:49:01PM *  1 point [-]

if you're going to excoriate everyone else for failing to "jettison [their] intuitive feelings in favor of cold, hard, abstract calculation", you should provide the actual cold, hard, abstract calculations supporting your own position.

I should have pointed this out earlier, but for the record: "cold, hard, abstract calculation" referred to the willingness to ignore quantitatively weak evidence even though it "feels important" to you; it did not refer to some specific back-of-the-envelope application of Bayes' Theorem.

(And "excoriate" is definitely not the right word here, at least with regard to the LW community.)

Comment author: 13 December 2009 07:21:50AM 3 points [-]

A condition is that you must account for the fact that most (let us say 80% for the purposes of your calculation) persons convicted of a crime in a democratic society are in fact guilty of it

I'm curious where in the world you get this "fact". I don't believe that at all (and it seems essentially unverifiable). Also, remember that Knox isn't a random person convicted of a crime: most of them don't make international news. Also, Italy does not have the same rights and freedoms as the US: for instance, they don't have separation of church and state.

Comment author: 13 December 2009 09:14:39AM 2 points [-]

The only test I can imagine is: when a new technique, like DNA testing, comes along, test a random sample of cases to which it is applicable. Unfortunately the cases re-examined are very carefully chosen, so no such information is available.

Comment author: 13 December 2009 07:32:40AM 1 point [-]
Comment author: 13 December 2009 07:46:00AM 0 points [-]

Thanks for that link. I don't understand why the plea bargain rate is at all relevant. Prosecutors try to dispose of most cases through plea bargaining, and paying a fine may be cheaper than paying legal costs for many people who plead guilty. I don't see any reason why an innocent person would be any less likely to plead guilty.

The innocence project focuses on high-profile murder and rape cases where DNA evidence can be obtained, so it's very non-representative of the criminal justice system as a whole.

Also, this ignores the question of legal justifications and excuses, and other defenses like illegally obtained evidence. If, as a matter of fact, you killed someone, but the evidence was obtained illegally, and you're still found guilty of murder, that's still a wrongful conviction.

Comment author: 13 December 2009 07:56:14AM 1 point [-]

The part relevant to my earlier post was:

"....even if juries get it right only 80 percent of the time (an assumption at which most sensible scholars would cringe).... But the real wrongful conviction rate is almost certainly lower, and significantly so ... ".

Comment author: 13 December 2009 05:05:29PM 1 point [-]

"I offer \$50 to the AK defense fund..."

Has the offer been amended from \$50,000 to \$50 since last night, or did I just misread it at 1:00 AM?

A shame, because I was looking forward to seeing the attempt.