Table II.

Quality (certainty) of evidence categories.*

High	⊕⊕⊕⊕	Very confident that the true effect lies close to that of the estimate of the effect.
Moderate	⊕⊕⊕○	Moderate confidence 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	⊕⊕○○	Limited confidence in the effect estimate: the true effect may be substantially different from the estimate of the effect.
Very Low	⊕○○○	Very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.

*Adapted from the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) (GRADE working group).