Appendix 2. USPSTF Quality Rating

Randomized Controlled Trials and Cohort Studies

Criteria:

• Initial assembly of comparable groups.
  1. For RCTs: adequate randomization, including first concealment and whether potential confounders were distributed equally among groups.
  2. 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, cross-overs, adherence, contamination).
• Levels of follow-up: 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:
  1. For RCTs: intention-to-treat analysis.
  2. For cohort studies: adjustment for potential confounders.

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 percent; 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 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. 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.

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