Table 2

Grading of recommendations assessment, development and evaluation system16

Code	Quality of evidence	Definition
A	High	Further research is very unlikely to change our confidence in the estimate of effect. Several high-quality studies with consistent results. In special cases: one large, high-quality multicentre trial.
B	Moderate	Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. One high-quality study. Several studies with some limitations.
C	Low	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. One or more studies with severe limitations.
D	Very low	Any estimate of effect is very uncertain. Expert opinion. No direct research evidence. One or more studies with very severe limitations.