Appendix Table 3. U.S. Preventive Services Task Force Quality Rating Criteria
| RCTs and Cohort Studies |
| Criteria |
| Initial assembly of comparable groups: RCTs—adequate randomization, including concealment and whether potential confounders were distributed equally among groups; 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 interventions |
| Important outcomes considered |
| Analysis: adjustment for potential confounders for cohort studies, or intension-to-treat analysis for RCTs |
| Definition of ratings based on above criteria |
Good: Studies will be rated "good" if they meet all criteria—comparable groups are assembled initially and maintained throughout the study (follow-up at least 80%); reliable and valid measurement instruments are used and applied equally to the groups; interventions are spelled out clearly; important outcomes are considered; and appropriate attention to confounders in analysis.
Fair: Studies will be graded "fair" if any or all of the following problems occur without the important limitations noted in the "poor" category below: Generally comparable groups are assembled initially but some question remains whether some (although not major) differences occurred in follow-up; measurement instruments are acceptable (although not the best) and generally applied equally; some but not all important outcomes are considered; and some but not all potential confounders are accounted for.
Poor: Studies will be graded "poor" if any of the following major limitations exists: Groups assembled initially are not close to being comparable or are not maintained throughout the study; unreliable or invalid measurement instruments are used or not applied equally among groups (including not masking outcome assessment); and key confounders are given little or no attention. |
| 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 results 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 (more than 100) broad-spectrum patients with and without disease
Fair: Evaluates relevant available screening test; uses reasonable although not best standard; interprets reference standard independent of screening test; moderate sample size (50 to 100) and a "medium" spectrum of patients
Poor: Has important limitation, such as use of inappropriate reference standard; improperly administered screening test; biased ascertainment of reference standard; very small sample size of very narrow selected spectrum of patients |
| Case-Control Studies |
| Criteria |
| Accurate ascertainment of cases |
| Nonbiased selection of case and control participants 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 above criteria |
| Good: Appropriate ascertainment of case participants and nonbiased selection of case and control participants; exclusion criteria applied equally to case and control participants; response rate equal to or greater than 80%; diagnostic procedures and measurements accurate and applied equally to case and control participants; and appropriate attention to confounding variables |
| Fair: Recent, relevant, without major apparent selection or diagnostic work-up bias, but with response rate less than 80% or attention to some but not all important confounding variables |
| Poor: Major selection or diagnostic work-up biases, response rates less than 50%, or inattention to confounding variables |
RCT = randomized, controlled trial.
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