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Table 11 Modified GRADE quality assessment criteria

From: Systems for grading the quality of evidence and the strength of recommendations II: Pilot study of a new system

Quality of evidence

Study design

Lower if *

Higher if *


Randomised trial

Study quality:

-1-Serious limitations

-2-Very serious limitations

-1-Important inconsistency


-1-Some uncertainty

-2-Major uncertainty

-1-Sparse data

-1-High probability of Reporting bias

Strong association:

+1-Strong, no plausible confounders, consistent and direct evidence**

+2-Very strong, no major threats to validity and direct evidence***

+1-Evidence of a Dose response gradient

+1-All plausible confounders would have reduced the effect


Quasi-randomised trial



Observational study


Very low

Any other evidence

  1. * 1 = move up or down one grade (for example from high to moderate)
  2. 2 = move up or down two grades (for example from high to low)
  3. The highest possible score is High (4) and the lowest possible score is Very low (1). Thus, for example, randomised trials with a strong association would not move up a grade.
  4. ** A relative risk of >2 (< 0.5), based on consistent evidence from two or more observational studies, with no plausible confounders
  5. *** A relative risk of > 5 (< 0.2) based on direct evidence with no major threats to validity