Anamorphic analysis: sampling and estimation for covariate effects when both exposure and disease are known.

When study subjects are obtained through sampling procedures based on the level of known characteristics, covariate data can be used to adjust effect estimates. This principle, which is well-understood for both exposure-based sampling (cohort studies) and disease-based sampling (case-control studies), can also be applied to cross-classifications of the source population. An opportunity for exposure--disease-based sampling arises whenever data on exposure and disease are both available on a group of subjects who are incompletely characterized in terms of other covariates. This is a common intermediate stage in epidemiologic studies of many kinds.