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HIV Risk and Prevention Estimates


This section of the CDC HIV Web site provides public health professionals and others with the state of the science regarding HIV prevention including estimates from the current scientific literature for HIV risk behaviors, effective prevention strategies to reduce the risk of acquiring or transmitting HIV, and factors increasing HIV risk. The estimates come from the published scientific literature and will be periodically updated as new research is completed.

If you are interested in learning more about your own risk of acquiring or transmitting HIV, you can also go to CDC’s HIV Risk Reduction Tool designed to help individuals make the best decisions for protecting themselves and their partners. We are currently evaluating this tool and welcome your feedback.

Principles for Selecting Estimates

Given different states of the science for the different prevention strategies reviewed, with a range of study designs (e.g., RCT, observational) and measurement methods used (e.g., self-report, blood levels of drug) in the literature, decision rules were made to be applied across strategies in an effort to select effectiveness estimates that were most closely aligned with each other and that most accurately represented effectiveness if the prevention strategy was actually used.  More detailed principles are listed below, and the rationale for each specific estimate that was chosen is provided within the tables.

The choice of estimate was prioritized based on the following criteria:

  • Only evidence based on peer-reviewed published reports was considered. Unpublished data, including conference abstracts, were not considered to be reliable because results may change as more data become available and data are re-analyzed or methods adjusted based on peer-review feedback. Additionally, the amount of information available for unpublished studies does not allow us to adequately assess methods and quality of data and analysis.
  • Only evidence regarding HIV transmission (e.g., HIV outcomes) was considered. Data for non-HIV outcomes (e.g., pregnancy prevention, STD prevention) were considered not to be good proxies for HIV transmission because modeling or other methods that require complex assumptions would be required to equate proxies with HIV transmission rates and introduce additional uncertainty.
  • For the consensus estimates, a hierarchy was established for prioritizing the type of estimate to select.
  • The greatest priority was given to estimates based on “verified use” of the strategy or interventions that were based on the most objective measure available for determining “verified use” (not selecting highest or optimal use but instead selecting based on any evidence of actual use).
  • If an objective measure for “verified use” was not available, then we chose the best subjective measure available (e.g., self-report) and prioritized the highest level of use reported based on subjective measure (e.g., consistent use or always using) recognizing that self-report may overestimate actual use.
  • If no analysis based on actual or level of use was available, then the mITT/ITT comparison of “assigned” versus “not assigned” was selected.
  • An estimate from a published meta-analysis was used if available and relevant for the strategy/risk factor in question; otherwise the most appropriate estimate from an RCT or observational study was used.


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