TABLE 2

Classification of Recommendations and Level of Evidence

Classification of Recommendations
 Class I: Conditions for which there is evidence and/or general agreement that a given procedure or treatment is beneficial, useful, and effective.
 Class II: Conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of a procedure or treatment.
  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: Conditions for which there is evidence and/or general agreement that a procedure/treatment is not useful/effective and in some cases may be harmful.
Level of Evidence
 Level of Evidence A: Data derived from multiple randomized clinical trials or meta-analyses.
 Level of Evidence B: Data derived from a single randomized trial or nonrandomized studies.
 Level of Evidence C: Only consensus opinion of experts, case studies, or standard-of-care.
  • Classification of Recommendations and Level of Evidence are expressed in the ACC/AHA format and described in more detail in Table 3.