Sammendrag
Background: "The study of the occurrende of disease" is a short but quite precise definition of epidemiology, as it includes both the descriptive and analytic approaches. Whereas descriptive studies of the distribution of diseases and their potential causal factors may generate hypotheses about disease aetiology, causal inferences may most safely be drawn from analytic testing through properly designed obervational studies. Methods: The most commonly used observational designs are the retrospective case-control and the prospective cohort studies. In some respects the two designs complement each other. Drawing on some classic epidemiologigal studies, their main properties in terms of what questions they may answer, what their applicabilities are, as well as their main strengths and weaknesses, are discussed.
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