Box 1: Criteria for rating therapeutic studies*61
ClassDescription
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:

    1. Concealed allocation

    2. Primary outcome(s) clearly defined

    3. Exclusion and inclusion criteria clearly defined

    4. 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

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

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

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