A.22 The probability that one beta variable is greater than another

Suppose π and ρ have independent beta distributions

Unnumbered Display Equation

Then

Unnumbered Display Equation

[see Altham (1969)]. For an expression (albeit a complicated one) for

Unnumbered Display Equation

see Weisberg (1972).

When α, β, γ and  are large we can approximate the beta variables by normal variates of the same means and variances and hence approximate the distribution of  by a normal distribution.

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