Table 1.

Levels of evidence/grades of recommendation

Levels of evidence

I. Evidence from at least one large randomized, controlled trial of good methodological quality (low potential for bias) or meta-analyses of well-conducted randomized trials without heterogeneity

II. Small randomized trials or large randomized 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; optional

D. Moderate evidence against efficacy or for adverse outcome, generally not recommended

E. Strong evidence against efficacy or for adverse outcome, never recommended