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probability is calculated incorrectly for OR and 1 of (XOR) #1501

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reteprelief opened this Issue Sep 7, 2018 · 1 comment

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reteprelief commented Sep 7, 2018

It should be
P(A or B) = P(A) + P(B) - P(A and B)
calculated as 1 - P(!A and !B) = 1 - (1 - P(A))*(1-P(B))

It currently calculates it as P(A) + P(B)
the NRC handbook calls this "rare event approximation" (see page VI-5) for P(A or B), which argues the probability is accurate to within about ten percent of the true probability when P(Ei) < 0.1.

@reteprelief reteprelief changed the title from probability is calculated incorrectly for OR to probability is calculated incorrectly for OR and 1 of (XOR) Sep 7, 2018

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reteprelief commented Sep 7, 2018

For XOR (1of) we calculated 1 - (1 - P(A))*(1-P(B))
Instead it should be
Sum(P(Xi)*P(!Xk in 1..n)) over set of events Xi and k <> i

@wafflebot wafflebot bot added the in progress label Sep 7, 2018

@wafflebot wafflebot bot added review and removed in progress labels Sep 7, 2018

@reteprelief reteprelief added this to the 2.3.6 milestone Sep 7, 2018

@wafflebot wafflebot bot removed the review label Sep 7, 2018

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