Table 1.

Levels of Evidence and Grades of Recommendation

Item	Definition
Level of Evidence
A. High quality	Further research is unlikely to change our confidence in the prediction of the effects. Consistent evidence from RCTs without significant limitations or from exceptionally strong evidence derived from observational studies.
B. Moderate quality	Further research is likely to have an important impact on our confidence in the prediction of the effects and may change the prediction. Evidence from RCTs with significant limitations (inconsistent results, methodologic flaws, indirect or imprecise) or very strong evidence from observational studies.
C. Low quality	Further research is very likely to have an important impact on our confidence in the prediction of the effects and is likely to change the prediction. Evidence for at least one critical outcome from observational studies, case series, or RCTs with serious flaws; indirect evidence; or a consensus among experts.
Grade of recommendation
1. Strong	Recommendation can apply to most patients in most circumstances. The desired effect is certainly greater than the harmful effect.
2. Weak	The best action may differ depending on the circumstances or patient or society values. Other alternatives may be equally reasonable. The desired effect may be slightly greater than the harmful effect.

RCTs, randomized controlled trials.