Class of Recommendation
I: Evidence and/or general agreement that a given diagnostic procedure/treatment is beneficial, useful, and effective
IIa: Conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of the treatment with the weight of evidence in favour
IIb: Conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of the treatment with the usefulness/efficacy less well established
III: Evidence that the treatment is not useful and in some cases may be harmful
Level 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 by experts and/or small studies, retrospective studies, and registries