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A
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Pairwise meta-analysis of comparative randomized controlled trials (RCTs) (for interventions)
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No important flaws
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Consistent
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Direct or strong indirect
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RCTs (for interventions)
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Non-randomized studies (for diagnosis and prognosis)
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B
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Meta-analysis of RCTs or RCTs (for interventions)
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Important flaw < OR > Inconsistent < OR > Weak indirect
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Non-randomized studies (for diagnosis or prognosis)
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Important flaw < OR > Inconsistent < OR > Weak indirect
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Non-randomized controlled studies (for interventions)
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No important flaws consistent direct < OR > Strong indirect
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C
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Non-randomized controlled studies (for interventions)
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Important flaw < OR > Inconsistent < OR > Weak indirect
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| |
Meta-analyses or RCTs with a combination of important flaws AND inconsistency AND/OR indirect evidence
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D
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Other evidence (not expert opinion)
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E
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Expert opinion
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Exceptions that can alter the quality of grading
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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
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Coding notes
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Important flaws occur when the highest standards of research that could be achieved by a study are not applied
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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
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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
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Summary of quality of evidence
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A. High quality of evidence – future evidence is unlikely to change confidence in the estimate of effect
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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
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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
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D. and E. Very poor quality evidence – Any estimate of effect is very uncertain
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