Recommendation grades and levels of evidence
| Grade | Evidence |
|---|---|
| A | At least one high quality meta-analysis, systematic review of RCTs or RCT with a very low risk of bias and directly applicable to the target population, or a body of evidence principally from well conducted meta-analyses, systematic reviews of RCTs, or RCTs with a low risk of bias, directly applicable to the target population and demonstrating overall consistency of results |
| B | A body of evidence from high quality systematic reviews of case-control or cohort studies or high quality case-control or cohort studies with a very low risk of confounding, bias, or chance and a high probability that the relation is causal, directly applicable to the target population, and demonstrating overall consistency of results; or extrapolated evidence from high quality meta-analyses, systematic reviews of RCTs, or RCTs with a very low risk of bias |
| C | A body of evidence from well conducted case-control or cohort studies with a low risk of confounding, bias, or chance and a moderate probability that the relation is causal, directly applicable to the target population and demonstrating overall consistency of results; or extrapolated evidence from high quality systematic reviews of case-control or cohort studies or high quality case-control or cohort studies with a very low risk of confounding, bias, or chance and a high probability that the relationship is causal |
| D | Evidence from non-analytic studies, eg, case reports, case series; evidence from expert opinion; or extrapolated evidence from case control or cohort studies with more than a very low risk of confounding, bias, or chance, and less than a high probability that the relation is causal |