Epidenmiologists employ stratified case-control studies nested within a defined cohort so that collection of costly covariate information, such as bioassays of stored tissue saamples, may be limmited to the most informative participants.These designs involve two-phase stratified samples: a simple random sample (the main cohort)from an infinite super-population (model) at Phase I; and a finite population stratified (case-control) sample at Phase II.One approach to analysis involves inverse probability weighting (IPW) of general estimating equations.