Ok. I agree with you that the post was confused and kind of incoherent at times. It was somewhere deep in it I ended up seeing what the author was talking abo

Ok. I agree with you that the post was confused and kind of incoherent at times. It was somewhere deep in it I ended up seeing what the author was talking about (taking his statements about physical evidence on faith for the sake of discussion). I'm definitely not saying that Ms Knox is innocent -- I don't know anything about the facts of that case, so we're only talking about the mathematical methodology here. I do think your definition of a prior is a bit off though... like, the choices around priors wouldn't be whether to use "did she do it" vs the imbalances of evidence or such. We're trying to estimate the likelihood of "did she do it," so the question is what do we use to do that? The prior probability of "she did it" has to be the probability that some random member of the 20/female/american/student general public will commit the murder, because we don't have anything more than that (as you said). Then, we update our estimate by looking at the available evidence (such as, "was found standing by door holding bleach mop," which would the viewed in terms of the likelihood that that would be observed and the statement 'she did not do it' being true) to come to our posterior probability, which is the estimate informed by all of the available evidence. As a side note, it's great when you can have a civil discussion on the internet. Maybe there's hope for HN after all.