Table 5.

Grading System Adopted from the Proposal by the U.S. Agency for Healthcare Policy and Research⁹³

	Description
Level of evidence
Ia	Evidence from a meta-analysis of randomized controlled trials
Ib	Evidence from at least one randomized controlled trial
IIa	Evidence from at least one controlled study without randomization
IIb	Evidence from at least one other type of quasi-experimental study
III	Evidence from observational studies
IV	Evidence from expert committee reports or experts
Grade of recommendation
A	Directly based on Category I evidence
B	Directly based on Category II evidence or extrapolated from Category I evidence
C	Directly based on Category III evidence or extrapolated from Category I or II evidence
D	Directly based on Category IV evidence or extrapolated from Category I, II, or III evidence