Casey Anthony - analyzing evidence using Bayes

Most people haven't weighed the evidence for the same reason I'm not motivated to do so - there's nothing in it for me. It helps that none of my friends talk about the case.

Someone made a very useful post like this for the Amanda Knox case

Link. ;-)

My gut feeling is that most people have not bothered to weight the evidence, but look at the surface layers of the case and judge based on questionable heuristics.

Indeed. My own more specific theory is that people -- this includes juries, by the way -- judge these cases by first sizing up the defendant's personality and deciding how much they sympathize with him or her (in almost all cases, the answer is "very little"), deriving a prior for guilt directly from that, and then looking at other evidence in the case to see whether it confirms this initial impression. This theory accounts nicely for the otherwise perplexing emphasis that people put on psychological evidence such as the defendant's "lies", both in the Knox case (where this negative impression is based on misinformation and misunderstanding) and in the Anthony case (where the defendant does appear to have behaved in an authentically unsympathetic fashion).

FWIW, my take on the case is that (from what I know from very limited media exposure) there is a substantial probability that Anthony is guilty of murder, well over 10%, possibly over 50%, but very likely well below the 99% or so that I would consider "beyond reasonable doubt". In this, the case is sharply distinguished from that of Knox, where in my view the hypothesis of guilt lacks sufficient evidence even to be considered.

Judging from what I read on wikipedia:

-She is clearly guilty of child neglect, making her more likely to be guilty of either murder or manslaughter

-The body is too far gone to see how the child died, and there are no witnesses or convincing dna evidence

-Overall, there is very little evidence that points in favour of either murder or manslaughter to the exclusion of the other

-Manslaughter has a higher prior probability than murder (especially when swimming pools are involved, which are responsible for about 25% of all deaths for children that age from what I've read)

-Therefore I find that probability (manslaughter or other cause) > probability (murder)

-Legally speaking, she can not be convicted of murder beyond reasonable doubt

-however, the probability of her being guilty of murder is still around 20%

-Legally speaking, she can not be convicted of manslaughter beyond reasonable doubt

-however, the probability of her being guilty of manslaughter is still around 65%

Thanks for posting this.

I don't know about Bayes but I think Occam's razor (simplest explanation for the data) indicates that most likely she's guilty of murder. Here are the relevant events (as evidence) that I'm thinking about:

• Casey Anthony borrowed a shovel from her neighbor on June 18th 2008. Cayley Anthony was last seen alive on June 15th 2008.

• There were search queries like chloroform, 'how to break a neck' (and others) found on Casey Anthony's computer - through reconstructed Firefox cache browser. The computer files were deleted to hide the data, so special software was used to reconstruct the data.

• There was a month between the last time Cayley Anthony was seen alive and the time she was reported as missing. When she was reported as missing, it was the grandmother, Casey Anthony's mother Cindy Anthony, who reported it.

• During that month, Casey Anthony was seen as partying and entering 'hot-body' contests.
• In Cindy Anthony's call to 911, she describes the stench in Casey Anthony's car as a foul smell 'as if someone died in there'.
• The body was found only a quarter a mile away from the house where here parents and Casey Anthony live.
• There was a duct tape with the skeletal remains of the body. Same type of duct tape was also found in Anthony household.

I could go on and on and on...

The jurors acquitted Casey Anthony on the basis that there was no connection between her and the dead body of the child and that prosecutors weren't able to prove a link between her and the dead body of the child.

My reaction is that if you look at all the circumstantial evidence, the simplest explanation that fits all the data is that she probably killed her child. Yes, you can have someone just curious about chloroform searching google. Yes, it may also have been food rotting in the car. Yes, Casey Anthony may have borrowed the shovel for gardening - but if you string together all these explanations, the final conjunction of all of them just becomes a lot less probable.