TABLE 1.

GRADE levels of quality of scientific evidence.

GRADE	Definitie
High	•High certainty that true effect of treatment is close to estimated effect
	•Further research is very unlikely to change our confidence in the estimate of effect
	•Randomized trials without serious limitations well-performed observational studies with very large effects (or other qualifying factors),
Moderate	•Moderate certainty that true effect is close to estimated effect
	•Further research is likely to have an important impact on our confidence in the estimate of the effect and may change the estimate
	•Randomized trials with serious limitations, well-performed observational studies yielding large effects
Low	•Low certainty that true effect is close to estimated effect
	•Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change
	•Randomized trials with very serious limitations, observational studies without special strengths or important limitations
Very low	•Any estimate of effect is very uncertain
	•Randomized trials with very serious limitations and inconsistent results
	•Observational studies with serious limitations, unsystematic clinical observations (e.g. case series or case reports.