Table 2.

Grading of Recommendations Assessment, Development and Evaluation system. Adapted from Guyatt et al. 2008 [31]

Grading	Publication type	Recommendations
High quality	Meta-analyses, systematic reviews of RCTs, or RCTs with a low risk of bias	Further research is very unlikely to change our confidence in the estimate of effect
Moderate quality	High quality systematic reviews of case control or cohort studies; High quality case control or cohort studies with a very low risk of confounding or bias and a high probability that the relationship is causal; Well-conducted case control or cohort studies with a low risk of confounding or bias and a moderate probability that the relationship is causal	Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate
Low quality	Case control or cohort studies with a high risk of confounding or bias and a significant risk that the relationship is not causal	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
Very low quality	Non-analytic studies, e.g. case reports, case series; Expert opinion	Any estimate of effect is very uncertain