Case Cohort Study
- Observational design that analyzes a subset of a larger cohort: all cases plus a random sample of non-cases.
- Less costly and faster than a full cohort study while aiming to detect exposure–outcome associations.
- Can be subject to selection bias and is not well suited for rare outcomes.
Definition
Section titled “Definition”A case-cohort study is a type of observational study in which a subset of individuals from a larger population, known as the cohort, are selected for analysis. The subset consists of individuals who have developed a specific outcome of interest (cases) and a random sample of individuals from the cohort who have not developed the outcome (non-cases or controls).
Explanation
Section titled “Explanation”In a case-cohort design the starting point is a defined cohort. From that cohort, researchers select all individuals who developed the outcome of interest (cases) and a randomly chosen sample of cohort members who did not develop the outcome (non-cases). Data on exposures or risk factors are collected for both groups and analyzed to assess whether an association exists between the exposure and the outcome. Compared with a full cohort study, a case-cohort study requires data collection on fewer individuals, reducing cost and time. Compared with a traditional case-control study, it can be more efficient at detecting associations because it is anchored in the original cohort.
Examples
Section titled “Examples”Smoking and lung cancer
Section titled “Smoking and lung cancer”Cohort: all individuals who have ever smoked cigarettes.
Selected: a sample of individuals who have developed lung cancer (cases) and a random sample of individuals who have not developed lung cancer (non-cases or controls).
Data collected: cigarette smoking habits, such as the number of cigarettes smoked per day and the duration of smoking, for both cases and non-cases.
Analysis: determine whether there is a statistically significant association between cigarette smoking and the development of lung cancer.
Obesity and type 2 diabetes
Section titled “Obesity and type 2 diabetes”Cohort: all individuals who are obese.
Selected: a sample of individuals who have developed type 2 diabetes (cases) and a random sample of individuals who have not developed type 2 diabetes (non-cases or controls).
Data collected: obesity-related factors, such as body mass index (BMI) and waist circumference, for both cases and non-cases.
Analysis: determine whether there is a statistically significant association between obesity and the development of type 2 diabetes.
Use cases
Section titled “Use cases”- Examining associations between exposures and outcomes within a defined population while reducing the resources required compared with a full cohort study.
Notes or pitfalls
Section titled “Notes or pitfalls”- Selection bias: the cases and non-cases may not be randomly selected from the entire cohort, which can lead to overestimation or underestimation of associations.
- Not suitable for rare outcomes: there may not be enough cases to adequately power the study.
Related terms
Section titled “Related terms”- Cohort study
- Case-control study
- Case (outcome)
- Control (non-case)