The problem of finding an optimum sampling strategy from the class of all linear unbiased strategies with a given expected sample size is considered. The paper deals with the properties of admissibility, completeness and strong admissibility of the Horvitz-Thompson strategies.
"Choice of an Optimum Sampling Strategy-1." Ann. Statist. 3 (3) 669 - 679, May, 1975. https://doi.org/10.1214/aos/1176343129