Table 2:

Interpretation of quality of evidence levels according to GRADE^a

Level of evidence	Definition
High ⊕⊕⊕⊕	We are very confident that the true effect corresponds to that of the estimated effect.
Moderate ⊕⊕⊕O	We are moderately confident in the estimated effect. The true effect is generally close to the estimated effect, but it may be slightly different.
Low ⊕⊕OO	Our confidence in the estimated effect is limited. The true effect could be substantially different from the estimated effect.
Very low ⊕OOO	We have very little confidence in the estimated effect. The true effect is likely to be substantially different from the estimated effect.

^aAdapted with permission from Balshem et al. GRADE guidelines: 3. Rating the quality of evidence. J Clin Epidemiol 2011; 64:401–6.