become cases. In a case-cohort study, efficiency is optimised by only obtaining additional exposure information for participants experiencing the outcome of interest and for members of a random sample (subcohort) selected from the entire cohort independent of the outcome. An added advantage is that this subcohort can be used as a comparison cohort for different outcomes of interest. Case-cohort studies can be designed within large cohorts with blood samples, DNA or other materials stored at baseline for later exposure measurement.
