Table 1.

Level of evidence grading.

Level of evidence	Definition
Level A (high quality)	Further research is very unlikely to change our confidence in the estimate of effect.
Level B (moderate quality)	Further research is likely to have an important impact on our confidence in the estimate effect.
Level C (low quality)	There is limited effect in the estimated effect: the true effect maybe substantially different than the estimated effect.
Level D (very low quality)	Any estimate of effect is very uncertain.