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Appendix Table 1. U.S. Preventive Services Task Force Hierarchy of Research Design and Quality Rating Criteria*

Hierarchy of research design

I: Properly conducted RCT
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 and quality category definitions

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

Definition of ratings from above criteria:

     Good: Recent, relevant review with comprehensive sources and search strategies; explicit and relevant selection criteria; standard appraisal of included studies; and valid conclusions
     Fair: Recent, relevant review that is not clearly biased but lacks comprehensive sources and search strategies
     Poor: Outdated, irrelevant, or biased review without systematic search for studies, explicit selection criteria, or standard appraisal of studies

studies
Criteria:

Accurate ascertainment of cases
Nonbiased selection of cases/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

Definition of ratings based on criteria above:

     Good: Appropriate ascertainment of cases and nonbiased selection of case and control participants, exclusion criteria applied equally to cases and controls, response rate equal to or greater than 80%, diagnostic procedures and measurements accurate and applied equally to cases and controls, and appropriate attention to confounding variables
     Fair: Recent, relevant, without major apparent selection or diagnostic work-up bias but with response rates less than 80% or attention to some but not all important confounding variables
     Poor: Major section or diagnostic work-up biases, response rates less than 50%, or inattention to confounding variables

Randomized, controlled trials and cohort studies
Criteria:

Initial assembly of comparable groups:

     For RCTs: 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, and contamination)
Important differential loss to follow-up or overall high loss to follow-up
Measurements: equal, reliable, and valid (includes masking of outcome assessment)
Clear definition of the interventions
All important outcomes considered

Definition of ratings based on above criteria:

     Good: Evaluates relevant available screening tests, uses a credible reference standard, interprets reference standard independently of screening test, reliability of test assessed, has few or handles indeterminate results in a reasonable manner, includes large number (.100) and broad spectrum of patients
     Fair: Evaluates relevant available screening tests, uses reasonable although not the best standard, interprets reference standard independent of screening test, moderate sample size (50-100 subjects) and a "medium" spectrum of patients
     Poor: Has fatal flaw, such as use of an inappropriate reference standard, screening test improperly administered, biased ascertainment of reference standard, or very small sample size or very narrowly selected spectrum of patients

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

Definition of ratings based on above criteria:

     Good: Evaluates relevant available screening test, uses a credible reference standard, interprets reference standard independently of screening test, reliability of test assessed, has few or handles indeterminate results in a reasonable manner, includes large number (.100) and broad spectrum of patients with and without disease
     Fair: Evaluates relevant available screening test, uses reasonable although not the best standard, interprets reference standard independently of screening test, moderate sample size (50-100 subjects) and a "medium" spectrum of patients
     Poor: Has fatal flaw, such as use of an inappropriate reference standard, screening test improperly administered, biased ascertainment of reference standard, or very small sample size or very narrowly selected spectrum of patients

Note: RCT = randomized, controlled trial.

* Go to references 29 and 30.

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