Table 1.

Grading of Recommendations, Assessment, Development, and Evaluation (GRADE)

	Criteria
Quality of evidence
High (A)	Further research is very unlikely to change our confidence in the estimate of effect.
Moderate (B)	Further research is likely to have an important impact on our confidence in the estimate of effect and could change the estimate.
Low (C)	Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Any change in estimate is uncertain.
Strength of recommendation
Strong (1)	Factors influencing the strength of the recommendation include the quality of the evidence, presumed patient-important outcomes, and cost.
Weak (2)	Variability in preference and values or relatively high uncertainty. Recommendation is made with less certainty or higher cost or resource consumption.

Of the quality levels of evidence, we excluded “very low quality (D),” which was originally included in the GRADE system, for convenience. (Guyatt GH, Oxman AD, Vist GE, Kunz R, Falck-Ytter Y, Alonso-Coello P, et al. GRADE: an emerging consensus on rating quality of evidence and strength of recommendations. BMJ 2008;336:924-926.)