Disproportionate sampling for population subgroups in telephone surveys

Population studies often seek to examine phenomena in important population subgroups or to compare results among these and other subgroups. When subgroups of interest comprise a relatively small percentage of the population and acceptable subgroup member lists are not available to serve as sampling frames, it may be prohibitively expensive even by telephone to screen through a sample of the entire population. This paper considers some statistical effects of estimation from a class of two-stratum telephone sample designs where part of the frame with a higher subgroup concentration is disproportionately sampled compared to the rest of the frame. Using proportionate sampling as a reference, the relative impact of this disproportionate design is determined for nominal and effective sample sizes, where the latter are tied to the effect of variation in sample weights that occurs in disproportionately allocated samples. Findings are illustrated using two recent telephone surveys. Whereas nominal subgroup sample sizes may be improved by disproportionate sampling, we conclude that both the survey designer and analyst should use this type of design cautiously in telephone surveys.