A<unk>  <unk>  is a scientific procedure most commonly used in testing medicines or medical procedures.<unk> s are considered the most reliable form of scientific evidence because it eliminates all forms of spurious causality.<unk> s are mainly used in clinical studies, but are also employed in other sectors such as judicial, educational, social research. Clinical<unk> s involve allocating treatments to subjects at random. This ensures that the different treatment groups are 'statistically equivalent'.
Sellers of medicines throughout the ages have had to convince their consumers that the medicine works. As science has progressed, public expectations have risen, and government health budgets have become ever tighter, pressure has grown for a reliable system to do this. Moreover, the public's concern for the dangers of medical interventions has spurred both legislators and administrators to provide an evidential basis for licensing or paying for new procedures and medications. In most modern health-care systems all new medicines and surgical procedures therefore have to undergo trials before being approved.
Trials are used to establish average efficacy of a treatment as well as learn about its most frequently occurring side-effects. This is meant to address the following concerns. First, effects of a treatment may be small and therefore undetectable except when studied systematically on a large population. Second, biological organisms (including humans) are complex, and do not react to the same stimulus in the same way, which makes inference from single clinical reports very unreliable and generally unacceptable as scientific evidence. Third, some conditions will spontaneously go into  remission, with many extant reports of miraculous cures for no discernible reason. Finally, it is well-known and has been proven that the simple process of administering the treatment may have direct  psychological effects on the patient, sometimes very powerful, what is known as the placebo effect.
Randomized controlled trial
Longitudinal study
Cohort study
Placebo-controlled studies
Longitudinal studies
Clinical trial
Cross-sectional study
Evidence-based design