Methods Table 2. Rating System Used to Rate the Level of the Evidence and Strength of the Recommendation for Each Recommendation

Recommendations are based on scientific evidence and expert opinion. Each recommended statement includes a Roman numeral (III, or III) that represents the level of the evidence that supports the recommendation, and a letter (AB, or C) that represents the strength of the recommendation.

Classification Description
Class I Conditions for which there is evidence and/or general agreement that a given diagnostic evaluation, 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 and efficacy of a diagnostic evaluation, procedure, or treatment
Class IIa Weight of evidence and/or opinion is in favor of usefulness and efficacy
Class IIb Usefulness and efficacy are less well established by evidence and/or opinion
Class III Conditions for which there is evidence and/or general agreement that a diagnostic evaluation, procedure, or treatment is not useful and effective or if it in some cases may be harmful
Level of Evidence Description
Level A* Data derived from multiple randomized clinical trials, meta-analyses, or equivalent
Level B* Data derived from a single randomized trial, nonrandomized studies, or equivalent
Level C Consensus opinion of experts, case studies, or standard of care
Adapted from the American College of Cardiology and the American Heart Association Practice Guidelines. (American Heart Association, 2014); (Shiffman, 2003)


*In some situations, such as for IFN-sparing HCV treatments, randomized clinical trials with an existing standard-of-care arm cannot ethically or practicably be conducted.  The US Food and Drug Administration (FDA) has suggested alternative study designs, including historical controls or immediate versus deferred, placebo-controlled trials. For additional examples and definitions see FDA link:  In those instances for which there was a single pre-determined, FDA-approved equivalency established, panel members considered the evidence as equivalent to a randomized controlled trial for levels A or B.


Reviewed June 2016.

You are using an outdated browser, please upgrade your browser or download Firefox or Chrome.