ASN-minimax double sampling plans by variables for a normally distributed
quality characteristic with unknown standard deviation and two-sided
specification limits are introduced. The plans base on the essentially
Maximum-Likelihood (ML) estimator p* and the Minimum Variance Unbiased (MVU)
estimator ^p of the fraction defective p. The operating characteristic (OC) for
the plans is determined by using the independent random variables p*_1, p*_2
and ^p_1, ^p_2, which relate to the first and second samples, respectively. The
maximum of the average sample number (ASN) of these plans is shown to be
considerably smaller than the sample size of the corresponding single sampling
plans.