Case-control studies--an efficient observational study design.

Case-control studies are an efficient research method for investigating risk factors of a disease. The method involves the comparison of the odds of exposure in a patient group with that of the odds of exposure in a control group. As only a minority of the population is included in the study, less time can be devoted to those who remain free of the disease of interest. The design of a case-control study can be complex due to the selection of the appropriate cases and controls. Cases can be identified in a prospective and retrospective manner from various sources. Controls can be obtained via the patient, random digit dialing or in a hospital and all at different points in the time period of the study. All options have their own advantages and disadvantages. Furthermore, different forms of bias, such as recall bias and selection bias, can occur. When appropriately designed, case-control studies can provide the same information as in a cohort study, in a more rapid and efficient manner. Copyright 2009 S. Karger AG, Basel.