Case–control study

Case–control study is a type of observational study in epidemiology that is often used to identify factors that may contribute to a medical condition by comparing subjects who have that condition/disease (the 'cases') with patients who do not have the condition/disease but are otherwise similar (the 'controls').

Overview

The case–control study design is often used in the study of rare diseases or as a preliminary study where little is known about the association between the risk factor and disease of interest. Compared to cohort studies, case–control studies are relatively quick and inexpensive, and they are particularly suitable for studying diseases with long latency periods.

Methodology

In a case–control study, an existing group of cases is defined at the start of the study. Then, a group of controls is selected to match the cases in terms of certain characteristics such as age, gender, or other variables. The exposure to the risk factor in each group is then retrospectively assessed.

Strengths and Weaknesses

Case–control studies have several strengths. They are efficient for rare diseases or diseases with a long latency period between exposure and disease manifestation. They are less costly and less time-consuming; they are advantageous when exposure data is expensive or hard to obtain. They are also advantageous when studying dynamic populations in which follow-up is difficult.

However, case–control studies also have inherent limitations. They are not suitable for studying rare exposures. Furthermore, the temporal sequence between exposure and outcome is not always clear. Recall bias, selection bias and observer bias are also of concern.

Examples

One of the most significant case–control studies was the Lung Health Study, which identified the link between tobacco smoking and lung cancer. Another notable case–control study was the British Doctors Study, which related tobacco smoking with various health effects including lung cancer and heart disease.

See also

• Cohort study
• Cross-sectional study
• Longitudinal study
• Observational study

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