<P> A case - control study is a type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute . Case - control studies are often used to identify factors that may contribute to a medical condition by comparing subjects who have that condition / disease (the "cases") with patients who do not have the condition / disease but are otherwise similar (the "controls"). They require fewer resources but provide less evidence for causal inference than a randomized controlled trial . We only get odds ratio from a case control study which is an inferior measure of strength of association as compared to relative risk . </P> <P> The case - control is a type of epidemiological observational study . An observational study is a study in which subjects are not randomized to the exposed or unexposed groups, rather the subjects are observed in order to determine both their exposure and their outcome status and the exposure status is thus not determined by the researcher . </P>

Difference between case control study and randomized control trial
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