Table 1

GRADE quality assessment criteria

Quality of evidence
Study design
Lower if *
Higher if *

High
Randomised trial
Study quality:
-1 Serious limitations
-2 Very serious limitations
-1 Important inconsistency
Directness:
-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
Moderate



Low
Observational study


Very low




* 1 = move up or down one grade (for example from high to intermediate) 2 = move up or down two grades (for example from high to low)

** A statistically significant relative risk of >2 (< 0.5), based on consistent evidence from two or more observational studies, with no plausible confounders

*** A statistically significant relative risk of > 5 (< 0.2) based on direct evidence with no major threats to validity

Schünemann et al. Health Research Policy and Systems 2006 4:21   doi:10.1186/1478-4505-4-21