The power for the testing H0: β1 = 0. v.s. H1 : β1 = 0.1. (a). The power as a, cut-point for defining the strata in term of σY, varies with sample size (n0, n1, n2) = (200, 100, 100); (b). The power as ρ, the fraction of SRS sample, varies with n = 400, n1 = n2, and a = 1.