Level

Description

I

Evidence obtained from a systematic review of all relevant randomized controlled trials.

II

Evidence obtained from at least one properly deigned randomized controlled trial.

III.1

Evidence obtained from well-designed controlled trials, not randomized.

III.2

Evidence obtained from comparative studies such as cohort studies, case control studies preferably from more than one center or research group.

III.3

Evidence obtained from multiple time series with or without the intervention. Dramatic results in uncontrolled experiments.

IV

Evidence from opinion of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees.