Classification of evidence levels
1 ++	High‐quality meta‐analyses, systematic reviews of randomized controlled trials or randomized controlled trials with very low risk of bias
1 +	Well‐conducted meta‐analyses, systematic reviews of randomized controlled trials or randomized controlled trials with low risk of bias
1–	Meta‐analyses, systematic reviews of randomized controlled trials or randomized controlled trials with high risk of bias
2 ++	High‐quality systematic reviews of case–control or cohort studies or high‐quality case–control or cohort studies with very low risk of confounding, bias or chance and high probability that the relationship is causal
2 +	Well‐conducted case–control or cohort studies with low risk of confounding, bias or chance and moderate probability that the relationship is causal
2–	Case–control or cohort studies with high risk of confounding, bias or chance and significant risk that the relationship is not causal
3	Non‐analytical studies, e.g. case reports, case series
4	Expert opinion
Grades of recommendation
A	At least one meta‐analysis, systematic review or randomized controlled trial rated as 1 ++ and applicable directly to the target population; or a systematic review of randomized controlled trials or a body of evidence consisting principally of studies rated as 1 + applicable directly to the target population and demonstrating overall consistency of results
B	Body of evidence including studies rated as 2 ++ applicable directly to the target population and demonstrating overall consistency of results; or extrapolated evidence from studies rated as 1 ++ or 1 +
C	Body of evidence including studies rated as 2 + applicable directly to the target population and demonstrating overall consistency of results; or extrapolated evidence from studies rated as 2 ++
D	Evidence level 3 or 4; or evidence extrapolated from studies rated as 2 +
Good practice point	Recommended best practice based on the clinical experience of the guideline development group