Table 1.

Classes and levels of evidence.

Class	Definition
Class I	Evidence or general agreement that a treatment or procedure is beneficial, useful, effective
Class II	Conflicting evidence or divergence of opinions about usefulness
Class II-A	Weight of evidence in favor of usefulness
Class II-B	Usefulness not well established
Class III	Evidence or agreement that a treatment or procedure is not useful or may be harmful
Level of evidence A	Data derived from multiple randomized studies or meta-analyses
Level of evidence B	Data derived from a single randomized trial or large non-randomized studies
Level of evidence C	Consensus expert opinion or small studies

Color, Level of evidence; Green: Class I, Yellow, Class II-A, Orange: Class II-B, Red, Class III.