Table A1.

Levels of Evidence and Grade of Recommendations

Level of Evidence	Source of Evidence	Grade of Recommendation	Rationale for Recommendation
Ia	Meta-analyses of randomized controlled trials	A	At least one randomized controlled trial of good quality and consistency addressing specific recommendation
Ib	At least one randomized controlled trial
IIa	At least one well-designed, nonrandomized study, including phase II trials and case-control trials	B	Well-conducted studies but no randomized controlled trials on topic of recommendation
IIb	At least one other type of well-designed, quasi-experimental study (ie, studies without planned intervention, including observational studies)
III	Well-designed, nonexperimental descriptive studies; meta-analyses or randomized controlled trials or phase II studies only published in abstract form
IV	Expert committee reports or opinions and/or clinical experience of respected authorities	C	Expert committee reports and/or clinical experience of respected authorities