handoflixue comments on Inherited Improbabilities: Transferring the Burden of Proof - Less Wrong

30 Post author: komponisto 24 November 2010 03:40AM

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Comment author: komponisto 24 November 2010 07:37:42PM *  0 points [-]

This assumes that the burglary being faked is the only piece of evidence

No; I fully grant that other evidence that Knox and Sollecito are guilty, if it exists, would be evidence of the burglary being fake, which would lower the burden of proof on that hypothesis.

However, that isn't how Massei and Cristiani reason. They don't say, in the section on the burglary (which is at the beginning of the report), "and since we know from all the other evidence that Knox and Sollecito are guilty, we can therefore easily use these arguments about glass patterns to confirm that they did in fact stage the burglary, in case you were wondering about that". And it's easy to see why they don't say that: there wouldn't be much point, because if they've already shown that Knox and Sollecito are guilty, their work is done! (*)

Instead, what they say is "these arguments about glass patterns etc. prove that the burglary was staged. Now, having established that piece of evidence against them (i,e. the staging of the burglary), let us now consider the other evidence, which, in combination with the burglary, will show how really guilty they are."

(* ) Technically, staging a burglary is itself an offense, so there may actually have been reason for them to proceed this way. But in that case the burglary issue would have come at the end of the report, not the beginning.

Comment author: handoflixue 24 November 2010 07:47:30PM 0 points [-]

"these arguments about glass patterns etc. prove that the burglary was staged. Now, having established that piece of evidence against them (i,e. the staging of the burglary), let us now consider the other evidence, which, in combination with the burglary, will give us an accurate probability on whether they are guilty"

I've bolded a single change to your quote. With that change made, do you feel this is a reasonable assertion?

Comment author: komponisto 24 November 2010 08:42:21PM *  0 points [-]

No. The error is in the first sentence

these arguments about glass patterns etc. prove that the burglary was staged.

They only (conceivably) prove the burglary was staged if you're already taking into account the rest of the evidence of murder.

Comment author: handoflixue 24 November 2010 08:56:21PM 0 points [-]

That's only true if you assume p(A=>B) is 1

Comment author: komponisto 24 November 2010 09:06:27PM *  0 points [-]

...or approximately 1.

(And by P(A=>B), I think you meant P(B|A), didn't you?)

Comment author: handoflixue 24 November 2010 09:14:07PM *  0 points [-]

P(Someone faked the burglary) != P(Amanda Knox faked the burglary). The report asserts the first, not the second, from my reading.

Given that "someone faked" is true, I think assigning an approximately 100% chance that Amanda Knox is guilty is rather seriously unfounded. What am I missing?

Comment author: komponisto 24 November 2010 09:19:58PM 0 points [-]

What am I missing?

That "burglary was faked" is shorthand for "burglary was faked by Knox and Sollecito" throughout this post and discussion. The latter is what Massei and Cristiani argue, and is what would most strongly imply that Knox and Sollecito are guilty of murder.

Comment author: handoflixue 24 November 2010 09:42:32PM 1 point [-]

The evidence you quoted merely suggests the burglary was faked. I'd assume there are more people with a motive to do that than just Knox and Sollecito? Why would we assume, with high enough certainty to convict, that it was certainly them and not a roommate, or someone who knew them?

Comment author: komponisto 24 November 2010 09:55:28PM *  0 points [-]

Look, I'm not saying Massei and Cristiani's argument that Knox and Sollecito staged the burglary is convincing, by any means!

That said, their argument that if the burglary was staged, the staging was done by Knox and Sollecito is probably the most convincing part of it. At the very least, they would have a highish prior, since they had access to the house and were "available" that night to do the staging if they wanted to.

Comment author: Jack 24 November 2010 10:37:38PM 0 points [-]

I figured this out but it threw me when I got to this part of the post. I'm not sure the convenience of the shorthand justifies throwing your readers off.