Table 1 Definitions for classification of evidence
| Rating of recommendation | Translation of evidence to recommendations | Rating of therapeutic article |
|---|---|---|
| RCT = randomized controlled trial. | ||
| 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 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 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 criterion 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 | |