Table 1

Levels of evidence and grades of recommendations

Levels of evidence
 IEvidence 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
 IISmall 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
 IIIProspective cohort studies
 IVRetrospective cohort studies or case-control studies
 VStudies without control group, case reports, experts opinions
Grades of recommendations
 AStrong evidence for efficacy with a substantial clinical benefit, strongly recommended
 BStrong or moderate evidence for efficacy but with a limited clinical benefit, generally recommended
 CInsufficient evidence for efficacy or benefit does not outweigh the risk or the disadvantages (adverse events, costs, …), optional
 DModerate evidence against efficacy or for adverse outcome, generally not recommended
 EStrong evidence against efficacy or for adverse outcome, never recommended