According to evidence-based medicine approach it is necessary to collect and use all available critically evaluated evidences to critically assess the specific achievements of modern medicine. Evidence can be obtained from a number of studies: randomized, controlled, or observational. As the observational study requires less investment, carried out more easily, but at the same time, is adequate to a high grades of evidence, we will discuss them in this paper. Cohort and case-control studies have the highest grade of evidence of all observational studies, so we will focus on them.
Keyword(s): Observational studies, cohort studies, case-control studies.
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