Key points are not available for this paper at this time.
Richard F. Potthoff, Max A. Woodbury, Kenneth G. Manton, "Equivalent Sample Size" and "Equivalent Degrees of Freedom" Refinements for Inference Using Survey Weights Under Superpopulation Models, Journal of the American Statistical Association, Vol. 87, No. 418 (Jun., 1992), pp. 383-396
Potthoff et al. (Mon,) studied this question.