“…A series of studies by statistical sampling theorists from the 1940s onward, fi rst reviewed by Buckland ( 1951 ), extended Cochran ' s idea of a superpopulation model to investigate statistical properties of estimators in spatial populations where systematic sampling was more precise (Quenouille 1949, Das 1950, Jowett 1952, Williams 1956, Hannan 1962, Iachan 1982, Bellhouse and Sutradhar 1988. However, this theoretical approach has not yet produced a robust, unbiased variance estimator generally usable with systematic data sets (see e.g., Cochran 1977 ).…”