Appendix Table 3. U.S. Preventive Services Task Force Hierarchy of Research Design and Quality Rating Criteria^a

Hierarchy of Research Design

I: Properly conducted randomized, controlled trial
II-1: Well-designed controlled trial without randomization
II-2: Well-designed cohort or case-control analytic study
II-3: Multiple time series with or without the intervention; dramatic results from uncontrolled experiments
III: Opinions of respected authorities, based on clinical experience; descriptive studies or case reports; reports of expert committees

Design-Specific Criteria

Systematic reviews

Criteria
   Comprehensiveness of sources considered/search strategy used
   Standard appraisal of included studies
   Validity of conclusions
   Recency and relevance are especially important for systematic reviews

Case-control studies

Criteria
   Accurate ascertainment of case-patients
   Nonbiased selection of case-patients/controls with exclusion criteria applied equally to both

Response rate
   Diagnostic testing procedures applied equally to each group
   Measurement of exposure accurate and applied equally to each group
   Appropriate attention to potential confounding variables

Randomized, controlled trials and cohort studies

Criteria
   Initial assembly of comparable groups
      For randomized, controlled trials: adequate randomization, including first concealment and whether potential confounders were distributed          equally among groups
      For cohort studies: consideration of potential confounders with either restriction or measurement for adjustment in the analysis;          consideration of inception cohorts
   Maintenance of comparable groups (includes attrition, crossovers, adherence, contamination)
   Important differential loss to followup or overall high loss to followup
   Measurements: equal, reliable, and valid (includes masking of outcome assessment)
   Clear definition of the interventions
   All important outcomes considered

Diagnostic accuracy studies

Criteria
   Screening test relevant, available for primary care, adequately described
   Study uses a credible reference standard, performed regardless of test results
   Reference standard interpreted independently of screening test
   Handles indeterminate result in a reasonable manner
   Spectrum of patients included in study
   Sample size
   Administration of reliable screening test

^aObtained from reference 67.

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