RobertLumley comments on Casey Anthony - analyzing evidence using Bayes - Less Wrong

2 Post author: Zachary_Kurtz 07 July 2011 05:19PM

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Comment author: RobertLumley 07 July 2011 07:14:34PM *  2 points [-]

The things that need to be distinguished are "guilty" and "committed murder". "Not guilty" and "innocent" are very, very different terms. I haven't met anyone who thinks she didn't commit the murder, but A. was there enough evidence to prove it, and B. Did the prosecution actually prove it? Maybe, and absolutely not.

The other thing that's bothered me as of late about a purely Bayesian approach is this: I'm reading Elizer's OB posts in order from the beginning, and I'm almost to 2008. Perhaps he addresses it at some point, but he hasn't yet in my reading. (I've also read the intuitive explanation, but having had three separate statistics classes, Bayes was a subject I understood pretty well to begin with.)

Shouldn't there be some accounting of the standard deviation of your estimate of your priors? If I have a prior that I've reached by amounting ten bits of evidence, that is quite different from a prior that I've reached by amounting one bit of evidence. I don't see how a traditionally Bayesian approach takes this into account.

(And sorry that's somewhat off topic, it's just bothered me for awhile now.)

Comment author: Cyan 08 July 2011 03:38:21AM 2 points [-]

Shouldn't there be some accounting of the standard deviation of your estimate of your priors? If I have a prior that I've reached by amounting ten bits of evidence, that is quite different from a prior that I've reached by amounting one bit of evidence. I don't see how a traditionally Bayesian approach takes this into account.

Check out Metauncertainty. The post Joys of Conjugate Priors gives a specific example.

Comment author: komponisto 08 July 2011 06:38:40PM 2 points [-]

Check out Metauncertainty.

That post should be linked to more often. It is fundamental for discussions of calibration. It should have been promoted, frankly.

Comment author: RobertLumley 08 July 2011 01:02:45PM 1 point [-]

Thanks, I'll read those when I get a chance.

Comment author: AnlamK 07 July 2011 07:25:30PM *  -1 points [-]

What exactly do people mean by 'proof'? With near certainty, almost nothing can be proven.

Since the body decomposed under the soil for 30 days, it's really hard to determine the precise case of death - even though I think some prosecution witnesses made the argument that it was a homicide. It's hard to link the murderer with the body, since the body was discovered so much later.

I think the prosecution had enough 'circumstantial evidence' to get a conviction. I think that beyond a reasonable doubt, Casey Anthony was responsible for the child's death. It may not have been murder but something happened to that child which this woman tried to cover up.

I know that the law works under the presumption of innocence but I wonder why prosecution was assumed to be under such burden of proof. Doesn't the defense also have a burden to explain the duct tape, the stench, etc.? Has the defense met that burden? I don't think so.

Comment author: RobertLumley 07 July 2011 07:58:03PM 0 points [-]

"Doesn't the defense also have a burden to explain the duct tape, the stench, etc.? Has the defense met that burden?"

In law, there is no such burden. It doesn't matter. The only thing the defense must prove is that the prosecution failed to prove their case. And 12 jurors who spent far more time in the courtroom than either you or I agreed that they did not. And did so quite quickly, as jury deliberations go. But the prosecution had no murder weapon, so solid motive, and no time of death. From what I've read (which is admittedly limited) they even did a poor job with cause of death.