Table 2

Category of evidence and strength of statements rating scales

Category of evidence
Diagnostic/prognostic studiesIntervention studies
1 The available evidence is strong and includes consistent results from well-designed, well-conducted studiesAt least one RCT or meta-analysis of RCT
2 The available evidence is sufficient to determine effects, but confidence in the estimate is constrained by such factors as: the number, size, or quality of individual studies, inconsistency of findings across individual studies, limited generalisability of findingsControlled (non-randomised) studies
3 The available evidence is insufficient due to the limited number or size of studies, important flaws in study design or methods, inconsistency of findings across individual studies, gaps in the chain of evidence, lack of information on important outcomesDescriptive studies, such as comparative studies, correlation studies, or case–control studies
Strength of statements
ABased on category 1 evidence
BBased on category 2 evidence, or extrapolated recommendations from category 1 evidence
CBased on category 3 evidence, or extrapolated recommendations from category 2 evidence
DExpert opinion or standard of care
  • RCT, randomised controlled trial.