Table 1.

Rating of evidence classification scheme

Rating of recommendationTranslation of evidence to recommendationsRating of therapeutic article
A—Established as effective, ineffective, or harmful for the given condition in the specified population.Level A rating requires at least one convincing Class I study or at least two consistent, convincing Class II studies.Class 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 dropouts and crossovers 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 population.Level B rating requires at least one convincing Class II study or at least three consistent Class III studies.Class 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 criteria a–d.
C—Possibly effective, ineffective, or harmful for the given condition in the specified population.Level C rating requires at least two convincing and consistent Class III studies.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.
U—Data inadequate or conflicting. Given current knowledge, treatment is unproven.Class IV: Evidence from uncontrolled studies, case series, case reports, or expert opinion.