Table 2. Recommendation grade and evidence strength.

Recommendation grade	Evidence strength	Comment
A	1	Systematic review (with homogeneity) of randomized controlled trials
B	2a	Systematic review (with homogeneity) of cohort studies
	2b	Exploratory cohort studies or randomized controlled trials of low quality
C	3	Systematic review (with homogeneity) of case-control studies, or individual case-control studies
	4	Case series and poor-quality case-control studies
D	5	Expert opinion, or inconsistent or non-determinative evidence from trials of any level of evidence quality