Table 5 Definitions for classification of evidence

Rating of recommendationTranslation of evidence to recommendationsRating of therapeutic article
RCT = randomized controlled trial.
A = Established as effective, ineffective, or harmful for the given condition in the specified populationLevel A rating requires at least one convincing class I study or at least two consistent, convincing class II studiesClass I: Prospective, randomized, controlled clinical trial with masked outcome assessment, in a representative population. The following are required: a) primary outcome(s) is/are clearly defined b) exclusion/inclusion criteria are clearly defined c) adequate accounting for drop-outs and cross-overs with numbers sufficiently low to have minimal potential for bias d) relevant baseline characteristics are presented and substantially equivalent among treatment groups or there is appropriate statistical adjustment for differences
B = Probably effective, ineffective, or harmful for the given condition in the specified populationLevel B rating requires at least one convincing class II study or at least three consistent class III studiesClass II: Prospective matched group cohort study in a representative population with masked outcome assessment that meets a–d above OR a RCT in a representative population that lacks one criterion a–d
Class III: All other controlled trials (including well-defined natural history controls or patients serving as own controls) in a representative population, where outcome assessment is independent of patient treatment
C = Possibly effective, ineffective, or harmful for the given condition in the specified populationLevel C rating requires at least two convincing and consistent class III studies
U = Data inadequate or conflicting; given current knowledge, treatment is unprovenClass IV: Evidence from uncontrolled studies, case series, case reports, or expert opinion