*Geek Box: Nested-Case Control Study
A nested case-control design is termed “nested” because the study participants are sampled from within a larger cohort. In a nested case-control design, the researchers identify cases of their exposure-outcome of interest – for example, blood cholesterol levels and coronary heart disease [CHD] – that have either already occurred, or as they occur in the prospective cohort.
These cases are then matched with healthy participants, usually between 2 to 5, that act as controls for each case of the outcome. The study would then compare the cases to the controls on a particular exposure of interest, e.g., blood cholesterol levels in the CHD cases compared to the healthy controls.
Nested case-control studies provide certain advantages, in particular being able to examine a select group of participants within a cohort with a more granular level of detail. However, they are best utilised to examine a very clearly defined exposure on a single defined outcome. Where there may be multiple outcomes of interest, the process of matching each case to several healthy controls can become burdensome and the efficiency of the nested-case control design is lost.