AIDS Forecasting:

Undercount of Cases and Lack of Key Data Weaken Existing Estimates

PEMD-89-13: Published: Jun 1, 1989. Publicly Released: Jun 26, 1989.

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Pursuant to a congressional request, GAO reviewed 13 existing national forecasts projecting future cumulative numbers of Acquired Immune Deficiency Syndrome (AIDS) cases to identify: (1) prediction variations and uncertainties; (2) types of forecasting models used; (3) the quality of the main types of data used in the models; and (4) a realistic range of estimates for the cumulative number of AIDS cases through 1991.

GAO found that forecast model approaches using: (1) extrapolation estimated 200,000 to 325,000 cumulative cases through 1991; (2) back-calculation predictions of individuals already infected with the human immunodeficiency virus (HIV) estimated 120,000 to 295,000 cases; (3) macro-level assumptions about the epidemic's future course predicted about 160,000 to 400,000 cases; and (4) micro-level examination of individual behaviors that contribute to the epidemic estimated about 25,000 cases. GAO also found that all forecasts relied on Centers for Disease Control (CDC) national AIDS surveillance data, which had quality problems deriving from: (1) limited definitions of AIDS; (2) diagnostic errors and restrictions; and (3) inaccurate or late state and local reporting to CDC. In addition, GAO found that: (1) micro-level simulations were the most comprehensive but least empirical type of model; (2) extrapolation models were the least comprehensive; (3) some models were based on questionable assumptions; and (4) few models adequately adjusted for the identified data problems. GAO believes that, if the existing forecasts were adjusted to compensate for data biases, the realistic range of forecasts would be 300,000 to 480,000 cases.

Recommendations for Executive Action

  1. Status: Closed - Implemented

    Comments: The Department of Health and Human Services' (HHS) studies have not been used to improve estimates of AIDS cases.

    Recommendation: The Secretary of Health and Human Services should require the Director, CDC, to conduct rigorous national studies of the net effect of biases in the national AIDS surveillance data to improve national estimates of the current and projected size of the epidemic.

    Agency Affected: Department of Health and Human Services

  2. Status: Closed - Implemented

    Comments: The agency concurs with the recommendation. Full-time equivalent staff members increased to 24 from 17, but 2 positions have not yet been filled.

    Recommendation: The Secretary of Health and Human Services should require the Director, CDC, to assess whether the CDC Surveillance Branch for tracking cases of AIDS and HIV-related diseases has sufficient staff and resources to plan, monitor, review, and disseminate such studies to the AIDS research community and forecasting models.

    Agency Affected: Department of Health and Human Services

  3. Status: Closed - Implemented

    Comments: The agency concurs with the recommendation. CDC is reviewing plans for expanding information on risk-group membership that is available for public use. Some improvements were made.

    Recommendation: The Secretary of Health and Human Services should require the Director, CDC, to incorporate additional information on risk-group membership into the CDC public use data set.

    Agency Affected: Department of Health and Human Services

  4. Status: Closed - Not Implemented

    Comments: This recommendation was not addressed by HHS in its response to the committee. The agency now says its lack of response was due to confusion about who within HHS was supposed to respond.

    Recommendation: The Secretary of Health and Human Services should review existing and ongoing empirical studies of individual risk-group behaviors as well as of HIV transmission and the current level of HIV infection to determine where additional data are most needed.

    Agency Affected: Department of Health and Human Services

 

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