Table 1 Recommendation grades and levels of evidence

Grade of recommendation

 Class I

Evidence is conclusive or, if not, there is a general consensus that a procedure or a treatment is safe and efficacious

 Class II

There is conflicting evidence or divergent opinion on safety, efficacy or utility of treatment or procedure

 Class IIa

Opinions are in favor of the treatment or procedure. The majority of experts approves

 Class IIb

Less well established efficacy, opinions are divergent

 Class III

There is evidence or consensus that the treatment or procedure is not useful, efficacious or may be harmful

Levels of evidence

 A

Multiple concordant well designed randomized clinical trials or robust meta-analyses of randomized clinical trials

 B

Data from less robust meta-analyses, a single randomized clinical trial or observational studies

 C

Expert opinion