Sequential Statistics

4.9: Confidence Intervals for P(X

4.9 Confidence Intervals for P(X

In reliability problems the parameter p which is the probability that one random variable is stochastically larger than the other is of much interest.

Sequential confidence interval for p=P(X has been considered by Govindarajulu (1974). Let (X, Y) have a bivariate normal distribution with an unknown mean vector and an unknown covariance-matrix. Assume that we observe pairs of observations (X i , Y i ), i=1, 2,...

Let D i =Y i ?X i , D n = Y n ? X n , where Y n and X n denote means of samples of size n. Then, it is well known that p= ? ( ? D / ? D ) where ? D =E(Y ?X), denotes the variance of (Y ?X). Whatever be the covariance structure of X and Y, a reasonable estimate of p is . Then, we have the following result. For the sake of simplicity, we shall suppress all the subscripts in ?, ?, s and .

Theorem 4.9.1

Let a 2=(1+ ? 2/2 ? 2) and . Then, we have


where the subscript n in D n is suppressed for the sake of implicity.

Proof

Let . First we will show that


Toward this, write where t lies between D and ?. However, since D converges to ?

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