Classes of recommendations
Class I	There is evidence and general agreement favoring the recommendation
Class IIa	There is divergence, but the majority approves
Class IIb	There are divergence and conflicting opinions
Class III	Not recommended

Levels of evidence
Level A	Multiple randomized controlled clinical trials
Level B	A single randomized controlled trial, non-randomized clinical trials or well-designed observational studies
Level C	The consensus opinion of experts