Table 2.

Quality of evidence.

	Quality of evidence	Study designs
A	High	Meta-analyses of randomized controlled trials Randomized controlled trials (≥2 trials)
B	Moderate	One randomized controlled trial Meta-analyses of non-randomized controlled trials Large, well-designed, non-randomized controlled trials
C	Low	Other study designs such as descriptive studies, retrospective studies
D	Very low	No evidence (experts' opinions)