Compute Bayes optimal spending function
sfabz(theta, psi, alpha = 0.05)value of theta being tested
a list of parameters for the spending function, including
mu, the prior expectation of E[y]
tau2, the prior variance of E[y]
sigma2 the variance of y
level of test
This function computes the value of s that minimizes the acceptance probability of a biased level-alpha test for a normal population with known variance, under a specified prior predictive distribution.