Table 1.

Level of evidence

Level	Evidence
I	Evidence from a systematic review or meta-analysis of all relevant RCTs (randomized controlled trials) or evidence-based clinical practice guidelines based on systematic reviews of RCTs or three or more RCTs of good quality that have similar results.
II	Evidence obtained from at least one well-designed RCT (eg, large multi-site RCT).
III	Evidence obtained from well-designed controlled trials without randomization.
IV	Evidence from well-designed case–control or cohort studies.
V	Evidence from systematic reviews of descriptive and qualitative studies (meta-synthesis).
VI	Evidence from a single descriptive or qualitative study.
VII	Evidence from the opinion of authorities and/or reports of expert committees.

Abbreviation: RCT, randomized controlled trial.