Levels of evidence |
I |
Evidence from at least one large randomised, controlled trial of good methodological quality (low potential for bias) or meta-analyses of well-conducted randomised trials without heterogeneity |
II |
Small randomised trials or large randomised trials with a suspicion of bias (lower methodological quality) or meta-analyses of such trials or of trials with demonstrated heterogeneity |
III |
Prospective cohort studies |
IV |
Retrospective cohort studies or case–control studies |
V |
Studies without control group, case reports, experts’ opinions |
Grades of recommendation |
A |
Strong evidence for efficacy with a substantial clinical benefit, strongly recommended |
B |
Strong or moderate evidence for efficacy but with a limited clinical benefit, generally recommended |
C |
Insufficient evidence for efficacy or benefit does not outweigh the risk or the disadvantages (adverse events, costs, etc.), optional |
D |
Moderate evidence against efficacy or for adverse outcome, generally not recommended |
E |
Strong evidence against efficacy or for adverse outcome, never recommended |