So we're probably talking about an order of magnitude increase in the base rate: more like 1/5 instead of 1/50.
I'll posit a factor of three.
(Incidentally, there was never any "first independent report" prior to this one...)
My bad, that was quite confusing of me, I mean the Massei(+Cristiani) report, which is independent of the police lab. Will fix. Thanks!
The sample in question (Trace B) tested negative for blood, as did every other sample taken from the blade.
IMHO irrelevant, Meridith's DNA is incriminating whether it's from blood or tissue, and whether any blood chemicals remained after cleaning in sufficient quantity to test positive.
(Various lab procedural criticisms)
Do you want to formally introduce a hypothesis that, LCN aside, this test was sloppier than the average test at the average lab? (Call this "ddk.slop") If so, one way to numerically assess would be to establish:
How sloppy do you think the test was, in terms of percentile? Are 10% of lab tests as or more sloppy than this one? 1%? Less?
How certain are you that the ddk.slop and its associated percentile is true? (FWIW I currently think this lab test is less sloppy than average.)
Then we can quantify your estimated shift to the base rate.
The sample in question (Trace B) tested negative for blood, as did every other sample taken from the blade.
IMHO irrelevant, Meridith's DNA is incriminating whether it's from blood or tissue, and whether any blood chemicals remained after cleaning in sufficient quantity to test positive.
Nonetheless, conditioned on Meredith's DNA being present, a negative blood test is surely significant evidence in favor of contamination over guilt, isn't it? If it was contamination, you would expect this with near certainty; whereas if the knife had been used to kill...
Recently, on the main section of the site, Raw_Power posted an article suggesting that we find "worthy opponents" to help us avoid mistakes.
As you may recall, Rolf Nelson disagrees with me about Amanda Knox -- rather sharply. Of course, the same can be said of lots of other people (if not so much here on Less Wrong). But Rolf isn't your average "guilter". Indeed, considering that he speaks fluent Bayesian, is one of the Singularity Institute's largest donors, and is also (as I understand it) signed up for cryonics, it's hard to imagine an "opponent" more "worthy". The Amanda Knox case may not be in the same category of importance as many other issues where Rolf and I probably agree; but my opinion on it is very confident, and it's the opposite of his. If we're both aspiring rationalists, at least one of us is doing something wrong.
As it turns out, Rolf is interested in having a debate with me on the subject, to see if one of us can help to change the other's mind. I'm setting this post up as an experiment, to see if LW can serve as a suitable venue for such an exercise. I hope it can: Less Wrong is almost unique in the extent to which the social norms governing discussion reflect and coincide with the requirements of personal epistemic rationality. (For example: "Do not believe you do others a favor if you accept their arguments; the favor is to you.") But I don't think we've yet tried an organized one-on-one debate -- so we'll see how it goes. If it proves too unwieldy or inappropriate for some other reason, we can always move to another venue.
Although the primary purpose of this post is a one-on-one debate between Rolf Nelson and myself, this is a LW Discussion post like any other, and it goes without saying that others are welcome and encouraged to comment. Just be aware that we, the main protagonists, will try to keep our discussion focused on each other's arguments. (Also, since our subject is an issue where there is already a strong LW consensus, one would prefer to avoid a sort of "gangup effect" where lots of people "pounce" on the person taking the contrarian position.)
With that, here we go...