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...
[comment split due to length]
Now, to the slippage issue:
As it happens, in the present case, the only material found in the small intestine was at the very end, near the ileocecal valve. At least, that is the implication of the wording of Ronchi's speculation (combined with the absence of any mention by Massei and Cristiani of material nearer to the duodenum):
(Sollecito appeal, p. 165)
Now, if your mistrust of the defense is sufficiently high, perhaps you're not willing to draw the same inference I have from this passage. However, I'm still interested in the impact it would have on your probability estimates if it were true. Suppose for the sake of argument that there wasn't anything in the small intestine, save a small amount at the ileocecal valve. How would that affect your beliefs? Are you willing to acknowledge a significant dependence of your opinion on the presence of material in "earlier" parts of the small intestine?
Apart from this, another thing this passage implies is that Ronchi's speculation about slippage was confined to the possibility of it having occurred at the autopsy, with the intestines uncoiled, in a situation where ligatures had not been applied (which we know to be contrary to the actual situation). He wasn't suggesting, in other words, that there may have been slippage due to the body having been moved by the killer(s). And if in fact the only material in the small intestine was at the ileocecal valve, then it is very unlikely indeed that material could have slipped through 5 meters of coiled intestine inside the victim's body, as the slippage hypothesis would in that case require.
But we do have data for other situations, and those data are what my prior is based on. What's your prior, and why is it better?
Incidentally, I was able to obtain a copy of the Hellmig et al. paper. Here is the study protocol:
\
The range in the Hellmig et al. study was 29-203 minutes.
Obviously, it depends crucially on what we know about the process that generated the numbers. Here we're talking about the duration of a physiological process, which is likely to be distributed approximately normally modulo specific pathological conditions. Of those numbers, the most relevant is the 82 (due to the use of a larger test meal with mixed food groups, and its taking place after the phenomenon described below was discovered).
Beyond differences in the test meal, the shorter times may be accounted for by a phenomenon known as "interdigestive duodenogastric reflux", which is a "sieving" process involving the shuffling of food back and forth between the stomach and duodenum, that takes place during the lag phase. This phenomenon was not known when some of the earlier studies were published, and so there is a significant possibility that those studies detected duodenal activity that the investigators mistook for the end of the lag phase. (HT to LondonJohn at JREF for this observation.)
But furthermore, we also have to reason about the hypothetical sequences of numbers that we didn't see. If the numbers had been
110, 125, 123, 182, 148
to say nothing of
100, 250, 230, 820, 480
-- or even if the studies consistently had extreme data points in the range of 300, regardless of their averages -- then the Massei-Cristiani theory would be in significantly better shape.
I was actually pointing out that an earlier temperature measurement would probably have permitted a narrower confidence interval.
But, since you mention it, 50-55 kg was just Lalli's eyeballed guess; the body was not actually weighed. Standard formulas predict 57-60 kg from Meredith's age, sex and height.
I agree, but I don't know whether other material would have been found if present. Is searching the entire small intestine feasible, and if so was such a search performed? Would food in the middle of the small intenstine after death have continued to digest?
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