Appendix Table 2. USPSTF Quality Rating Criteria

Randomized Controlled Trials (RCTs)

Criteria:

• Initial assembly of comparable groups: adequate randomization, including first concealment and whether potential confounders were distributed equally among groups.
• Maintenance of comparable groups (includes attrition, crossovers, adherence, contamination).
• Levels of followup: differential loss between groups; overall loss to followup.
• Measurements: equal, reliable, and valid, and including masking of outcome assessment.
• Clear definition of interventions.
• Important outcomes considered.
• Analysis: intention-to-treat analysis.

Definition of ratings based on above criteria:

Good: Meets all criteria: comparable groups are assembled initially and maintained throughout the study; followup at least 80%; reliable and valid measurement instruments applied equally to the groups; interventions clearly defined; important outcomes are considered; and appropriate attention to confounders in analysis. In addition, for RCTs, intention-to-treat analysis is used.

Fair: Generally comparable groups assembled initially, but some question remains whether some (although not major) differences occurred in followup; 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. Intention-to-treat analysis is done for RCTS.

Poor: Groups assembled initially are not close to being comparable or maintained throughout the study; measurement instruments are unreliable or invalid or not applied at all equally among groups; outcome assessment not masked; and key confounders are given little or no attention. For RCTs, no intention-to-treat analysis.

Case-Control Studies

Criteria:

• Accurate ascertainment of cases.
• Nonbiased selection of cases and 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 above criteria:

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: Appropriate ascertainment of cases and controls and exclusion criteria applied equally to cases and controls, and without major apparent selection or diagnostic work-up bias; 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.

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