Case-control study

Tarani Chandola, CCSR.

A case-control study is a type of observational study design that is often used in epidemiology. Two groups of people are compared; one with the condition/disease (‘cases’) and a similar group of people who do not have the condition or disease (‘controls’).

The proportion of each group having a history of a particular exposure or characteristic of interest is then compared. If there is a greater proportion of cases who are exposed to a particular factor compared to controls, there is an association between the exposure and the disease.

Case control studies are usually cheaper and easier to do than longitudinal and experimental study designs but they suffer from a number of biases including recall bias in a person’s recollection of their history of exposure to the factor of interest.

Figure: Schematic diagram of case-control study design. Kenneth F. Schulz and David A. Grimes (2002) Case-control studies: research in reverse. The Lancet Volume 359, Issue 9304, 431 - 434

A nested case control study utilises data from a longitudinal cohort study to select a subset of matched controls to compare with the incident cases. In a case-cohort study, all incident cases in the cohort are compared to a random subset of participants who do not develop the disease of interest. In contrast, in a nested-case-control study, some number of controls are selected for each case from that case's matched risk set.

By matching on factors such as age and selecting controls from relevant risk sets, the nested case control model is generally more efficient than a case-cohort design with the same number of selected controls. This is similar to propensity score matching techniques.

Experts/users at Manchester

• Dr Roger Webb
• Professor Jane Worthington

Key references

• Doll R, Hill AB (1952) A study of the aetiology of carcinoma of the lung. British Medical Journal 2:1271–1286
• Rothman K (2002) Epidemiology. An Introduction. Oxford University Press, Oxford, England
• Schulz KF, Grimes DA (2002) Case-control studies: research in reverse;. Lancet: 359: 431–34

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