Key points are not available for this paper at this time.
Gay C. Kitson, Marvin B. Sussman, Gwendolyn K. Williams, Randi B. Zeehandelaar, Barbara K. Shickmanter, Jeanne L. Steinberger, Sampling Issues in Family Research, Journal of Marriage and Family, Vol. 44, No. 4, Methodology: The Other Side of Caring (Nov., 1982), pp. 965-981
Kitson et al. (Mon,) studied this question.