PhilGoetz comments on Open Thread, September, 2010-- part 2 - Less Wrong

3 Post author: NancyLebovitz 17 September 2010 01:44AM

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Comment author: PhilGoetz 28 September 2010 04:33:50PM *  2 points [-]

I was wrong, and jimrandomh was right. I said:

P(X|A,B) = 1-(1-P(X|A))(1-P(X|B)) if P(A,B) = P(A)P(B)

But P(X|A,B) = 1-P(~X|A,B)

therefore P(~X|A,B) = (1-P(X|A))(1-P(X|B)) = P(~X|A)P(~X|B)

This is equivalent to claiming P(X|A,B) = P(X|A)P(X|B)

And this is wrong for most distributions.