Morendil comments on Bayesian analysis under threat in British courts - Less Wrong

10 Post author: whpearson 03 October 2011 04:06PM

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Comment author: Morendil 03 October 2011 05:34:40PM *  9 points [-]

Don't read just the article, go see also the actual judgment (HT ciphergoth; pdf). I won't say "read it" because it's the kind of thing that may not be worth reading entire, but at least skim it to get a feel for what's actually being argued.

My sense of it is that the judge is saying "stats should not be allowed when the numbers on which they're based are 'merely' quantifying someone's uncertainty, rather than be anointed by scientists". Which is still silly, as it ignores that "scientific" stats do nothing other than quantify uncertainty; but it doesn't say "Ban Bayes".

Comment author: MatthewW 03 October 2011 07:28:22PM 4 points [-]

Thanks for the link.

I think paragraphs 80 to 86 are the key paragraphs.

They're declaring that using a formula isn't allowed in cases where the numbers plugged into the formula are themselves uncertain.

But in this case, where there was uncertainty in the underlying data the expert tried to take a conservative figure. The judges don't seem to think that helps, but they don't say why. In particular, para 108 iv) seems rather wrongheaded for this reason.

(It looks like one of the main reasons they overturned the original judgement was that the arguments in court ended up leaving the jury hearing less conservative estimates of the underlying figures than the ones the expert used (paras 103 and 108). That seems like a poor advertisement for the practice of keeping explicit calculations away from the jury.)