In addition to the prospective design that minimises systematic error introduced by recall bias, advantages of the InterAct case-cohort design include the time- and cost-efficiency and maximal sharing of resources that can be achieved by sharing of the randomly selected subcohort. In a traditional prospective cohort study such as EPIC, initially disease free individuals are followed up over time to observe the rate of occurrence of binary clinical events (e.g. diabetes) in relation to information obtained at baseline. The major advantage is that this approach avoids the problem of recall bias, but it involves follow-up of a large study population over many years and is time consuming and expensive. This is especially true when the characterisation of possible exposures is expensive and inefficient since it is obtained in the whole cohort, only a small proportion of which go on to 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
