A case-cohort study is similar to a nested case-control study in that the cases and non-cases are within a parent cohort; cases and non-cases are identified at time \(t_1\), after baseline. In a case-cohort study, the cohort members were assessed for risk factors at any time prior to \(t_1\). Non-cases are randomly selected from the parent cohort, forming a subcohort. No matching is performed.
Advantages of Case-Cohort Study:
Similar to nested case-control study design:
- Efficient– not all members of the parent cohort require diagnostic testing
- Flexible– allows testing hypotheses not anticipated when the cohort was drawn \((t_0)\)
- Reduces selection bias – cases and noncases sampled from the same population
- Reduced information bias – risk factor exposure can be assessed with investigator blind to case status
Other advantages, as compared to nested case-control study design:
- The subcohort can be used to study multiple outcomes
- Risk can be measured at any time up to \(t_1\) (e.g. elapsed time from a variable event, such as menopause, birth)
- Subcohort can be used to calculate person-time risk
Disadvantages of Case-Cohort Study:
As compared to nested case-control study design:
- Increased potential for information bias because
- subcohort may have been established after \(t_0\)
- exposure information collected at different times (e.g. potential for sample deterioration)
Statistical Analysis for Case-Cohort Study:
Weighted Cox proportional hazards regression model (we will look at proportional hazards regression later in this course)