Table 2.

Definition of levels of evidence [13]

A (high):	We are very confident in the estimate of the effect
B (moderate):	We are moderately confident in the estimate of the effect: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different
C (low):	Our confidence in the estimate of the effect is limited: the true effect may be substantially different from the estimate of the effect
D (very low):	We have very little confidence in the estimate of the effect: the true effect is likely to be substantially different from the estimate of effect