Epidemiologic designs have been developed to extract more information from fewer people, by judicious sampling strategies. Two-stage sampling, for example, was developed as a strategy for situations where a rare exposure is under study, and one can improve efficiency dramatically, particular for studying interactions, by over-sampling exposed cases and exposed controls and adjusting for the covariate- and outcome-dependent sampling fractions in the analysis. [4; 5] Pooling of specimens is another strategy that has been proposed as a way to include many more study subjects by minimizing assay costs, when interaction is of interest and exposure is assessed by a biomarker [6].
