Class I:	Evidence and/or general agreement that a given treatment or procedure is beneficial, useful, and effective.
Class II:	Conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of the given treatment or procedure.
Class IIa:	Weight of evidence/opinion is in favor of usefulness/efficacy.
Class IIb:	Usefulness/efficacy is less well established by evidence/opinion.
Class III:	Evidence or general agreement that the given treatment or procedure is not useful/effective and in some cases may be harmful.