Case-Control Study

Case-control studies measure the association between the exposure to particular risk factors and the occurrence of a specific disease. These types of studies are common in public health and medical research. The basic premise of such studies is the comparison of two groups: "cases," individuals who have a particular disease of interest to the researcher, and "controls," who do not have the disease.

In case-control studies, individuals in the case group are selected and matched to persons in the control group on a common set of characteristics that are not considered to be risk factors for the disease being studied. These characteristics are frequently demographic variables such as age, gender, education, income, and area of residence. Comparisons across the case-control pairs are made, examining hypothesized risk factors for a particular disease. For example a case-control study of heart disease among women may compare cases and controls on their level of exposure to factors thought to influence the risk of heart disease such as family history of heart disease, smoking, cholesterol, high blood pressure, diet, and exercise. These differences are usually assessed using statistical tests.

Data for case-control studies is typically collected by interviewing or surveying the cases and the controls. Individuals in both groups are asked the same series of questions regarding their medical history and exposure to factors that are considered to increase the risk of developing the disease in question. Data may also be collected from medical records.

The advantages of case-control studies include the following:

• Data collection does not typically require medical tests or other intrusive methods.
• The studies are typically inexpensive to conduct in comparison to other methods of data collection.
• They are good for examining rare diseases because the investigator must identify cases at the start of the research rather than waiting for the disease to develop.
• Case-control studies allow for the examination of several risk factors for a particular disease at the same time.

As with all research studies, there are some significant disadvantages as well, including the following:

• Data on exposure and past history is subject to the individual's memory of events.
• It can be difficult to confirm and/or measure the amount of exposure to a particular risk factor of interest.
• Defining an appropriate control group can be difficult, especially if the risk factors for a particular disease are not well defined.
• Case-control studies are not good for diseases that result from very rare risk factors (rare exposures) unless there is a high correlation between the disease and the exposure.