Nested Case Control Study
- Efficient way to study associations when following an entire cohort is impractical or costly.
- Cases and controls are drawn from the same cohort, improving comparability of background characteristics.
- Commonly used when the outcome of interest is rare; may have limited representativeness of the larger population.
Definition
Section titled “Definition”A nested case-control study is a type of observational study that involves selecting a subgroup of individuals from a larger cohort and comparing their characteristics and exposures to a group of controls.
Explanation
Section titled “Explanation”A nested case-control study selects a subset of participants from an existing cohort. Researchers collect baseline information (for example, exposures and other factors), follow the cohort for several years, and identify incident cases of the outcome of interest. For each identified case, a control (or controls) who did not develop the outcome is selected from the same cohort. This design is often used when it is impractical or costly to follow the entire cohort for a long period of time, or when the outcome of interest is rare and occurs infrequently in the population. Because cases and controls come from the same cohort, they tend to be more similar in background characteristics, which can reduce potential confounding. The design also requires fewer resources than a full cohort study.
Examples
Section titled “Examples”Diet and breast cancer risk
Section titled “Diet and breast cancer risk”Researchers select a large cohort of women and collect information on dietary habits and other factors that may affect breast cancer risk. They follow this cohort for several years and identify any cases of breast cancer that occur. For each case, they select a control group of women from the same cohort who did not develop breast cancer, and compare the dietary habits of the two groups to see if there are any differences that may be associated with breast cancer risk.
Air pollution and respiratory illness
Section titled “Air pollution and respiratory illness”Researchers select a large cohort of individuals living in different areas with varying levels of air pollution. They collect information on respiratory health and other factors that may affect respiratory illness risk. They follow this cohort for several years and identify any cases of respiratory illness that occur. For each case, they select a control group of individuals from the same cohort who did not develop respiratory illness, and compare the air pollution levels in the areas where they live to see if there is a relationship between air pollution and respiratory illness risk.
Use cases
Section titled “Use cases”- When it is impractical or costly to follow the entire cohort for a long period of time.
- When the outcome of interest is rare and occurs infrequently in the population.
Notes or pitfalls
Section titled “Notes or pitfalls”- Cases and controls are selected from a smaller subgroup of the overall cohort, so the study sample may not be representative of the larger population.
Related terms
Section titled “Related terms”- Observational study
- Cohort study
- Case-control study