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Table 2 A summary of the GRADE approach to grading the quality of evidence for each outcome

From: Developing clinical practice guidelines: types of evidence and outcomes; values and economics, synthesis, grading, and presentation and deriving recommendations

Source of body of evidence Initial rating of quality Factors that may decrease the quality Factors that may increase the quality Final quality of a body of evidence *
Randomised trials High 1. Risk of bias 1. Large effect High
   2. Inconsistency 2. Dose–response ( or A)
   3. Indirectness 3. All plausible residual confounding would reduce the demonstrated effect or would suggest a spurious effect if no effect was observed Moderate
   4. Imprecision ( or B)
Observational studies Low 5. Publication bias Low
    ( or C)
    Very low
     ( or D)
  1. *Quality of evidence definitions.
  2. High: Further research is very unlikely to change confidence in the estimate of effect.
  3. Moderate: Further research is likely to have an important impact on confidence in the estimate of effect and may change the estimate.
  4. Low: Further research is very likely to have an important impact on confidence in the estimate of effect and is likely to change the estimate.
  5. Very low: Any estimate of effect is very uncertain.