This paper will explore the concepts of the choice of controls in observational analytic epidemiological case-control studies. An overview of the objects and basic concepts of case-control methodology along with a brief review of its historical development are presented. The definition and purpose of the control group are reviewed. The control's opportunity of exposure to the study variables is examined. Major sources of bias are reviewed and some solutions, emphasizing the control, are offered. Examples of case-control studies from neuromusculoskeletal literature are evaluated.
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