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. |