Table 3.

Rating the Quality of Evidence Using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) System.^a

Level of Evidence	Quality Rating	Explanation of Quality Rating
A	High	High level of confidence in the effects of the intervention.
		• Several high-quality studies with consistent outcomes
B	Moderate	Confidence in the effects of the intervention may change with future research findings
		• Only one high-quality study or
		• Several lower quality studies
C	Low	Confidence in the effects of the intervention is very likely to change with future research findings
		• All studies have severe limitations
D	Very low	Uncertainty about the effects of the intervention
		• Only expert opinion and/or
		• No research evidence or
		• Very low-quality evidence

^a Source: GRADE Working Group 2007 (modified by the EBM Guidelines Editorial Team)
http://www.essentialevidenceplus.com/product/ebm_loe.cfm?show=grade