komponisto comments on The Cameron Todd Willingham test - Less Wrong

3 Post author: Kevin 05 May 2010 12:11AM

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Comment author: Yvain 06 May 2010 07:45:01PM *  3 points [-]

Now that you mention it directly, it's flabbergasting that no one's ever said what percentage level "beyond a reasonable doubt" corresponds to (legal eagles: correct me if I'm wrong). That's a pretty gaping huge deviation from a properly Bayesian legal system right there.

Comment author: komponisto 06 May 2010 08:09:09PM *  2 points [-]

Well, the number could hardly be made explicit, for political reasons ("you mean it's acceptable to have x wrongful convictions per year?? We shouldn't tolerate any at all!").

In any case, let me not be interpreted as arguing that the legal system was designed by people with a deep understanding of Bayesianism. I say only that we, as Bayesians, are not prevented from working rationally within it.

Comment author: JRMayne 07 May 2010 03:15:13PM 1 point [-]

This is the third time on LW that I've seen the percentage of certainty for convictions conflated with the percentage of wrongful convictions (I suspect it's just quick writing or perhaps my overwillingness to see that implication on this particular post). They're not identical.

Suppose we had a quantation standard of 99% certainty and juries were entirely rational actors, understanding of the thin slice 1% is, and given unskewed evidence. The percentage of wrongful convictions would be well under 1% at trial; juries would convict on cases from 99% certainty to c. 100% certainty. The actual percentage of wrongful convictions would depend on the skew of the cases in that range.

Comment author: komponisto 07 May 2010 04:27:55PM *  0 points [-]

Yes, the certainty level provides a bound on the number of wrongful convictions. A 99% certainty requirement means at least 99% certainty, so an error rate of at most 1%.