TABLE 1. Rating Levels of Evidence and Recommendations

M
Classification of Recommendations
    Class IConditions for which there is evidence for and/or general agreement that the procedure or treatment is useful and effective.
    Class IIConditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of a procedure or treatment.
        IIaThe weight of evidence or opinion is in favor of the procedure or treatment.
        IIbUsefulness/efficacy is less well established by evidence or opinion.
    Class IIIConditions for which there is evidence and/or general agreement that the procedure or treatment is not useful/effective and in some cases may be harmful.
Level of Evidence
    Level of Evidence AData derived from multiple randomized clinical trials.
    Level of Evidence BData derived from a single randomized trial or nonrandomized studies.
    Level of Evidence CConsensus opinion of experts.