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

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



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


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.