| I |
Randomized controlled clinical trial (RCT) in a representative population Masked or objective outcome assessment Relevant baseline characteristics are presented and substantially equivalent between treatment groups, or there is appropriate statistical adjustment for differences Also required: Concealed allocation Primary outcome(s) clearly defined Exclusion and inclusion criteria clearly defined Adequate accounting for dropouts (with at least 80% of enrolled participants completing the study) and crossovers with numbers sufficiently low to have minimal potential for bias
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| II |
Cohort study meeting criteria a–d (see class I) or an RCT that lacks 1 or 2 criteria b–d (see class I) All relevant baseline characteristics are presented and substantially equivalent among treatment groups, or there is appropriate statistical adjustment for differences Masked or objective outcome assessment
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| III |
Controlled studies (including well-defined natural history controls or patients serving as their own controls) A description of major confounding differences between treatment groups that could affect outcome Outcome assessment masked, objective or performed by someone who is not a member of the treatment team
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| IV |
Did not include patients with the disease Did not include patients receiving different interventions Undefined or unaccepted interventions or outcome measures No measures of effectiveness or statistical precision presented or calculable
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