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Table 1 Grading of the quality of the evidence based on the GRADE system

From: Safe prescribing of non-steroidal anti-inflammatory drugs in patients with osteoarthritis – an expert consensus addressing benefits as well as gastrointestinal and cardiovascular risks

Nature of evidence Study design Study execution Consistency Directness of evidence
A Pairwise meta-analysis of comparative randomized controlled trials (RCTs) (for interventions) No important flaws Consistent Direct or strong indirect
RCTs (for interventions)
Non-randomized studies (for diagnosis and prognosis)
B Meta-analysis of RCTs or RCTs (for interventions) Important flaw < OR > Inconsistent < OR > Weak indirect
Non-randomized studies (for diagnosis or prognosis) Important flaw < OR > Inconsistent < OR > Weak indirect
Non-randomized controlled studies (for interventions) No important flaws consistent direct < OR > Strong indirect
C Non-randomized controlled studies (for interventions) Important flaw < OR > Inconsistent < OR > Weak indirect
  Meta-analyses or RCTs with a combination of important flaws AND inconsistency AND/OR indirect evidence
D Other evidence (not expert opinion)
E Expert opinion
Exceptions that can alter the quality of grading
Sparse data (few events); use of data not in its initial randomization or apparent publication bias can lower the quality; a very strong association can raise the quality
Coding notes
Important flaws occur when the highest standards of research that could be achieved by a study are not applied
Consistency occurs at two levels – design: consistent methods, patients, outcomes; and statistical: a test of homogeneity of a summary estimate when the level of design consistency is acceptable and meta-analysis appropriate
Directness – direct evidence: relevant patient benefits and harms are measured in studies; strong indirect: the surrogate endpoint is strongly related to desirable endpoints, or direct evidence is available for a sufficiently related patient group; weak indirect: the relationship between the study outcomes and patient benefits or harms is insufficient
Summary of quality of evidence
A. High quality of evidence – future evidence is unlikely to change confidence in the estimate of effect
B. Moderate quality of evidence – future evidence is likely to have an impact on the confidence of the estimate of effect and may change that estimate
C. Poor quality evidence – future evidence is very likely to have an impact on the confidence of the estimate of effect and is likely to change that estimate
D. and E. Very poor quality evidence – Any estimate of effect is very uncertain
  1. Developed from Lomas J, 1991 [71].