Table 1.

Grades of evidence and classes of recommendations

	Description
Grade of evidence
A	Data derived from multiple randomized, controlled trials or meta-analyses
B	Data derived from a single randomized trial or nonrandomized studies
C	Evidence based on clinical experience, descriptive studies, and opinion of respected authorities where further research is highly likely to impact confidence on the estimate of clinical effect
Class of evidence
I	Conditions for which there is evidence and/or general agreement that a given diagnostic evaluation, procedure, or treatment is beneficial, useful, and effective
II	Conditions for which there is conflicting evidence and/or divergence of opinion about the usefulness/efficacy of a diagnostic evaluation, procedure, or treatment
IIa	Weight of evidence/opinion is in favor of the usefulness/efficacy
IIb	Usefulness/efficacy is less well-established by evidence/opinion
III	Conditions for which there is evidence and/or general agreement that a diagnostic evaluation/procedure/treatment is not useful/effective and in some cases, may be harmful