Table 1

Key to evidence statements and grades of recommendations

Levels of evidence
1++High quality meta-analyses, systematic reviews of randomised controlled trials (RCTs) or RCTs with a very low risk of bias
1+Well-conducted meta-analyses, systematic reviews or RCTs with a low risk of bias
1−Meta-analyses, systematic reviews or RCTs with a high risk of bias
2++

  • 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

2+Well-conducted case–control or cohort studies with a low risk of confounding or bias and a moderate probability that the relationship is causal
2−Case–control or cohort studies with a high risk of confounding or bias and a significant risk that the relationship is not causal
3Non-analytic studies (eg, case reports, case series)
4Expert opinion
Grades of recommendations
AAt least one meta-analysis, systematic review or RCT rated as 1++ and directly applicable to the target population; or A body of evidence consisting principally of studies rated as 1+, directly applicable to the target population, and demonstrating overall consistency of results
BA body of evidence including studies rated as 2++, directly applicable to the target population, and demonstrating overall consistency of results; or Extrapolated evidence from studies rated as 1++ or 1+
CA body of evidence including studies rated as 2+, directly applicable to the target population and demonstrating overall consistency of results; or Extrapolated evidence from studies rated as 2++
DEvidence level 3 or 4; or Extrapolated evidence from studies rated as 2+
Good practice points
√Recommended best practice based on the clinical experience of the guideline development group