Abstract
Classes of Recommendation Class I: Conditions for which there is conclusive evidence and, failing that, general agreement that a given procedure is safe and useful/effective. Class II: Conditions for which there is conflicting evidence and/or a divergence of opinion about the safety and usefulness/efficacy of a procedure. Class IIa: Weight or evidence/opinion in favor of the procedure. Most approve. Class IIb: Safety and usefulness/efficacy less well established, with divergence of opinions. Class III: Conditions for which there is evidence and/or general agreement that a procedure is not useful/effective and, in some cases, may be harmful. Levels of Evidence Level A: Data derived from multiple large, concordant randomized trials and/or robust meta-analyses of randomized trials. Level B: Data derived from less robust meta-analyses, from a single randomized trial and/or from observational studies. Level C: Data derived from consensus opinion of experts.