Nested case control study

Nested case control matching

The difference between sampling from the whole population and only the non-diseased is that the whole population contains people both with and without the disease of interest. This means that a sampling strategy that uses the whole population as its source must allow for the fact that people who develop the disease of interest can be selected as controls. All cases who developed the outcome of interest during the follow-up are selected and compared with a random sample of the cohort. This topic is covered in more detail in EP Intermediate Epidemiology. As with cohort studies, case-control studies can be prospective or retrospective. However, case-control studies, like cohort studies, can be either retrospective or prospective. Alternatively, none of the cases might have already occurred, and new cases will be enrolled prospectively. When case-control studies were first developed, most were conducted retrospectively, and it is sometimes assumed that the rare-disease assumption applies to all case-control studies.

This means that a sampling strategy that uses the whole population as its source must allow for the fact that people who develop the disease of interest can be selected as controls. In essence, a case-control strategy was used, but it was conducted within the context of a prospective cohort study.

Wayne W.

nested case-control studies use subjects drawn from a cohort study

Several studies have used standard cohort analyses to study precursors to breast cancer, e. The difference between sampling from the whole population and only the non-diseased is that the whole population contains people both with and without the disease of interest.

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It is helpful to remember that it seems natural that the population denominator includes people who develop the disease in a cohort study. However, note that in comparison to the cases, there are so many controls that each particular control contributes relatively little information to the analysis.

In other words the cohort represents the source population that gave rise to the cases.

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Nested case control study