one tool in Evidence Based Medicine

The study design that provides the most compelling evidence of a causal relationship between the treatment and the effect, is the randomized controlled trial. Observational studies in epidemiology such as the cohort study and the case-control study are clinical studies in that they involve human participants, but provide less compelling evidence than the randomized controlled trial. The major difference between clinical trials and observational studies is that, in clinical trials, the investigators manipulate the administration of a new intervention and measure the effect of that manipulation, whereas observational studies only observe associations (correlations) between the treatments experienced by participants and their health status or diseases. These are fundamental distinctions in Evidence Based Medicine. http://en.wikipedia.org/wiki/Clinical_trial

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