CASE-CONTROL STUDYINTRODUCTIONThe simplest and most frequently used analytical strategy in epidemiology involves the case-control study. It mainly aims to establish the causes of diseases by studying the associations between exposure to a risk factor and the appearance of the disease. A case-control study is useful as the first step in finding a cause of adverse health effects. In the early stages of an etiology, exposure may be suspected, but the evidence may not be available or may not be strong enough to suggest an association. The case control will help by comparing people with the disease (cases) and people without the disease (controls) and will explore the variety of exposure or characteristics that cause the disease. A case control is designed to determine whether an exposure is associated with an outcome. A case-control study is a retrospective study because it begins with an outcome and then works backwards to view or investigate the exposure. The proportion of exposed and unexposed cases and controls was determined. Steps in Case-Control Study Start with the cases. Determine the exposures. Are the observed exposures higher than expected? A comparison group (controls) is needed to find what is expected.Table 1 : Design of a case-control study. Case selection Cases with disease Controls without disease Measuring past exposure Exposed Unexposed Total bcd a+c b+d Proportion exposed a/a+cb/b+d Table 1 describes how a case control study is conducted. First, the selection of cases with disease and controls without disease and past exposure is measured by eit...... middle of paper ...... n-hospitalized can be selected from several sources in the community, school lists, a list of insurance companies or a check for each case of a resident of an area, for example the neighbors in which the case lives. Such controls can be used for many years. Due to the security issue, such an approach poses a problem. So, instead of going house to house or door to door, an alternative method for this approach is to select orders from random dialing, as telephone exchanges generally correspond to neighborhood boundaries. This approach is mainly developed. country. Another approach is to use a best friend as a control, with a witness chosen in this approach likely having the same age, demographic, and social characteristics as the case. A spouse or siblings may be chosen as controls, as siblings may have some genetic difference between cases and controls..