Table 2.

GRADE quality criteria (GRADE=Grading of Recommendations Assessment, Development and Evaluation) (21)

Study Design	Quality of Evidence	Reduced Factors	Increased Factors
Randomized trials	High	Risk of bias	Large effect
		−1 serious	+1 large
		−2 very serious	+2 very large
	Moderate	Inconsistency	Dose response
		−1 serious	+1 if gradient
		−2 very serious
		Indirectness	Confounding
		−1 serious	+1
		−2 very serious
Observational studies	Low	Imprecision
		−1 serious
		−2 very serious
	Very low	Publication bias
		−1 likely
		−2 very likely