Table III.

Grades of recommendation and levels of evidence (see ref. 6)

Grade	Level	Type of evidence
A	Ia	Evidence obtained from meta-analysis of randomized-controlled trials.
	Ib	Evidence obtained from at least one randomized-controlled trial.
B	IIa	Evidence obtained from at least one well-designed controlled study without randomization.
	IIb	Evidence obtained from at least one other type of well-designed quasi-experimental study.
	III	Evidence obtained from well-designed non-experimental descriptive studies, such as comparative studies, cohort and case–control studies.
C	IV	Evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities.