Table 1.

Grading of Recommendations Assessment, Development and Evaluation quality criteria

Quality of evidence	Study design	Factors lowering the quality of evidence	Factors increasing the quality of evidence
High	Randomized trial	Study quality:	Strong association:
Moderate		−1: serious limitations	+ 1: strong, no plausible confounders
Low	Observationalstudy	−2: very serious limitations	+2: very strong, no major threats to validity
Very low	Any other evidence	−1: important inconsistency	+ 1: evidence of a dose response gradient
		Directness:	+ 1: allplausible confounders would have reduced the effect
		−1: some uncertainty
		−2: major uncertainty
		−1: sparse or imprecise data
		−1: high probability of reporting bias