Table 1.

Classes of recommendation and levels of evidence

Classes of recommendations
Class I	Evidence and/or general agreement that a given treatment or procedure is beneficial, useful, effective (is recommended/is indicated)
Class IIa	Weight of evidence/opinion is in favor of usefulness/efficacy (should be considered)
Class IIb	Usefulness/efficacy is less well established by evidence/opinion (may be considered)
Class III	Evidence or general agreement that the given treatment or procedure is not useful/effective, and in some cases may be harmful (is not recommended)

Levels of evidence
A	Data derived from multiple randomized clinical trials or meta‐analyses
B	Data derived from a single randomized clinical trial or large nonrandomized studies
C	Consensus of opinion of the experts and/or small studies, retrospective studies, registries