Table 1.

Levels of evidence and grades of recommendation [11].

Level of Evidence		Grades of Recommendation
Level	Description	Grade	Description
1	Meta-analysis or Systematic reviews of randomised controlled trials (RCT) or RCT with a low risk of bias	A	At least one meta-analysis, systematic review or RCT with a low risk of bias
2	High qualify systematic reviews of cohort studies, high-quality cohort studies or well-conducted cohort studies	B	High qualify systematic reviews of cohort studies, high quality cohort studies or extrapolated from RCT with a low risk of bias
3	Non-analystic studies e.g. institutional series	C	Well-conducted cohort studies or extrapolated from high qualify systematic reviews of cohort studies or high quality cohort studies
4	Expert opinion	D	Level 3 or 4 or extrapolated from well-conducted cohort studies