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Table 1 Quality assessment criteria according to GRADE adopted after reference[16]

From: Thresholds for statistical and clinical significance in systematic reviews with meta-analytic methods

Study design Levels of confidence in estimate Decrease confidence estimate if Increase confidence estimate if
Randomised clinical trials High Risk of bias Large intervention effect
One level if serious One level if large
   Two levels if very serious Two levels if very large
  Moderate Imprecision Dose response
   One level if serious One level if evidence of dose response
   Two levels if very serious  
Observational studies Low Indirectness All plausible confounding
   One level if serious One level if confounding would reduce a demonstrated effect
   Two levels if very serious  
  Very low Heterogeneity All plausible confounding
One level if serious One level if confounding would suggest a spurious effect when results show no effect
   Two levels if very serious  
   Publication bias  
One level if serious
   Two levels if very serious