ABSTRACT
A fundamental distinction in evidence-based medicine is between observational studies and randomized controlled trials. Types of observational studies in epidemiology such as the cohort study and the case-control study provide less compelling evidence than the randomized controlled trial. In observational studies, the investigators only observe associations between the treatments experienced by participants and their health status or diseases.

Keywords: Clinical Trials, Drugs, Diagnostics, Devices, Therapy Protocols.