Table IV.

Criteria for assessing the strength (quality) of evidence

Strength (quality) of evidence
High	Consistent, directly applicable result from one or more well-designed and well-executed randomized controlled trials (RCTs). This means that further research is very unlikely to change confidence in the estimate of effect
Moderate	Evidence derived from RCTs with important limitations (i.e. study bias, large loss to follow-up, lack of blinding, unexplained heterogeneity), indirect evidence derived from similar (but not identical) study populations, and studies with a very low number of patients or observed events (endpoints) In addition, evidence is available as derived from well-designed, controlled non-randomized studies, well-designed cohort studies or case-control studies as well as multiple interventional or non-interventional case series. This means that further research is likely to have an important impact on confidence in the estimate of effect and may change the estimate
Low	Observational studies, typically of poor quality due to the risk of errors. This means that further research is likely to have an important impact on confidence in the estimate of effect and is likely to change the estimate
Very low	Evidence is contradictory and/or of poor quality and/or unavailable, and therefore the risk-benefit ratio cannot be established. This means that any estimate of impact is uncertain as evidence, unavailable and/or inconclusive