Table 2

GRADE approach to rating the certainty of evidence12 14

GRADE categories of certainty of evidence
HighThe true effect lies on one side of a particular threshold, or in a particular range
ModerateAuthors are moderately confident that the true effect lies on one side of a particular threshold, or in a particular range: The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different and not within in the particular range or beyond the threshold.
LowAuthors’ confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect and not within in the particular range or beyond the threshold.
Very lowAuthors have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of the effect and not within in the particular range or beyond the threshold.
Domains that can reduce the COEDomains that can increase the COE

  • Limitations in study design and execution

  • Inconsistency in results

  • Indirectness of evidence (PICO and applicability)

  • Imprecision

  • Publication bias

  • Dose-response gradient

  • Large magnitude of effect

  • All plausible confounding would reduce the demonstrated effect or increase the effect if no effect was observed*

  • *This domain becomes part of the ‘limitations in study design and execution’ domain if Risk Of Bias In Non-randomised Studies of Interventions is used to assess risk of bias.

  • COE, certainty of evidence; GRADE, Grading of Recommendations, Assessment, Development and Evaluation; PICO, population-intervention-control-outcome.