Skip directly to local search Skip directly to A to Z list Skip directly to navigation Skip directly to site content Skip directly to page options
CDC Home

PRS Efficacy Criteria for Best-Evidence (Tier I) Risk Reduction (RR) Individual-level, Group-level, and Couple-level Interventions (ILIs/GLIs/CPLs)

Intervention Description

  • Clear description of key aspects of the intervention

Quality–Study design

  • Prospective study design
  • Appropriate and concurrent comparison arm
  • Random or minimally biased assignment of subjects to study arms

Quality–Study implementation and analysis

  • Follow-up assessment ≥ 3-months post completion of intervention for each study arm with recall not referring to pre-intervention period)
  • At least a 70% retention rate at a single follow-up assessment for each study arm
  • Comparison between intervention arm and an appropriate comparison arm
  • Analysis of participants subjects in study arms as originally allocated regardless of contamination or logistic/implementation issues
  • Analysis of participants regardless of the level of intervention exposure
  • Use of appropriate cluster-level analyses if assigned to study arms by cluster or group
  • Analysis must be based on post-intervention levels or on pre-post changes in measures
    • For pre-post changes used in analysis, measures must be identical, including identical recall period
  • Analysis based on an α =.05 (or more stringent) and a 2-sided test
  • With nonrandomized assignment, either no statistical differences in baseline levels of the outcome exist or baseline differences are controlled for in the analysis
  • Analytic sample ≥ 50 participants per study arm

Strength of Evidence–Significant positive intervention effects

  • Positive and statistically significant (p ≤.05) intervention effect for ≥1 relevant outcome measure
    • A positive intervention effect is defined as a greater reduction in HIV/STD incidence or risk behaviors or a greater increase in HIV protective behaviors in the intervention arm relative to the comparison arm
    • A relevant outcome is defined as a behavior (e.g., abstinence, mutual monogamy, number of sex partners, consistent condom use with anal/vaginal sex, unprotected anal/vaginal sex, proportion of anal/vaginal sex acts protected, injection drug use, sharing or borrowing needles/works) - that directly impacts HIV risk or a biologic measure indicating HIV or STD infection (i.e., HIV or STD incidence)
  • Effect at the follow-up and based on the analyses that meet study implementation and analysis criteria

Strength of Evidence–Negative intervention effects

  • No negative and statistically significant (p < .05) intervention effect for any relevant outcome
    • A negative intervention effect is defined as a greater increase in HIV/STD incidence or risk behaviors or a greater decrease in HIV protective behaviors in the intervention arm relative to the comparison arm.
  • No other statistically significant harmful intervention effect
  • For an intervention with a replication evaluation, no significant negative intervention effects in the replication study

Additional Limitations to Evaluate:

  • No evidence that additional limitations resulted in a fatal flaw:
    • A fatal flaw has occurred when the overall evaluation of limitations indicates they resulted in considerable bias, thus substantially reducing the confidence of the findings.
    • Examples of item limitations to check for possible fatal flaw:
      • Effects only found within potentially biased subset analyses;
      • Substantial missing data. Missing data plus loss to attrition exceeds acceptable limits for retention alone (≥ 40%)
      • Study arm non-equivalence: statistically significant differences between arms in important baseline demographics or risk factors
      • Differential retention: (1) significant difference between study arms in characteristics among retained or attritted participants; OR (2) more than minimal rate of differential retention (>10%)
      • Intervention activities did not match with the intervention concepts or guiding theories intended to produce the desired outcomes § Did not clearly describe issues related to generalizability
      • Too many post hoc analyses (even with Bonferroni corrections)
      • Inconsistent findings

All criteria must be satisfied for an intervention to be considered as a best-evidence individual-level, group-level, or couple-level intervention.

Source: Lyles et al. (2006) and Lyles at al. (2007).

Back to Efficacy Criteria

Top of Page


Get Tested

Find an HIV testing site near you.

Search location, such as: "Atlanta, GA", or "30033".

For more information, please visit

Please contact with any comments, suggestions, or concerns.

Syndicate This Content Podcast button Tell us what you think button CDC-INFO The U.S. Government's Official Web PortalDepartment of Health and Human Services
Centers for Disease Control and Prevention   1600 Clifton Road Atlanta, GA 30329-4027, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC–INFO