Table 1.

Levels of evidence

Level A: Two or more clinically controlled, randomize, double-blind studies carried out according to good clinical practice (GCP) versus placebo or versus an active drug for which there is proven evidence of efficacy

Level B: One clinically controlled study according to GCP or more than one controlled case–control study/ies or Cohort study/ies

Level C: Favourable judgement of two-thirds of the Ad Hoc Committee, historical controls, non-randomized studies, case reports