Table 2  Grading of the quality of evidence based on the GRADE system.

GRADE	Beschreibung	Symbol
High quality	“We are very confident that the true effect lies close to that of the estimate of the effect.”	⊕⊕⊕⊕
Moderate quality	“We are moderately confident in the effect estimate: The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.”	⊕⊕⊕⊖
Low quality	“Our confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect.”	⊕⊕⊖⊖
Very low quality	“We have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of effect.”	⊕⊖⊖⊖