Table 2.

Quality of evidence and its definition in the GRADE system

Quality of evidence	Definition
High quality (A)	We are very confident that the true effect lies close to the estimate of the effect. Further research is very unlikely to change our confidence in the estimate of effect
Moderate quality (B)	We are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is still a possibility that it is substantially different, further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate
Low quality (C)	Our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Further research is very likely to have an important impact on our confidence and is likely to change the estimate
Very low quality (D)	We have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect. Any estimate of effect is very uncertain