Class I: Prospective, randomized, controlled clinical trial with masked outcome assessment, in a representative population. The following are required:
primary outcome(s) is/are clearly defined exclusion/inclusion criteria are clearly defined adequate accounting for drop-outs and cross-overs with numbers sufficiently low to have minimal potential for bias relevant baseline characteristics are presented and substantially equivalent among treatment groups or there is appropriate statistical adjustment for differences
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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. |
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Class III: All other controlled trials (including well-defined natural history controls or patients serving as own controls) in a representative population, where outcome is independently assessed, or independently derived by objective outcome measurement. |
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Class IV: Evidence from uncontrolled studies, case series, case reports, or expert opinion |
