The following are details of the 3 methods for calculating the number of persons living with HIV/AIDS or AIDS.

Method 1—Ryan White CARE Act Formula

The legislative authority for the method for calculating the number of persons living with AIDS under Title I is Section 2603(a)(3)(c) of the Ryan White CARE Act. The legislative authority for the Title II estimation of the number of persons living with AIDS is Section 2618(2)(d). The same set of survival weights is used for Title I and Title II. The survival weights are updated by CDC according to methods specified in the Ryan White CARE Act. The weights calculated for this report are

Year 1—.41
Year 2—.54
Year 3—.62
Year 4—.66
Year 5—.72
Year 6—.76
Year 7—.79
Year 8—.84
Year 9—.88
Year 10—.92

The estimates from the Ryan White CARE Act formula for this report are based on AIDS cases reported to CDC through December 2004. AIDS cases reported during the preceding 120 months are aggregated into ten 12-month periods, and 10 “survival” weights are applied to the 10 AIDS case counts. For example, the first year count is multiplied by .41, the second year is multiplied by .54, and so on for all 10 counts. The summary count (total of these 10 weighted counts), which results from this computational formula, is the estimated number of persons living with AIDS in the state or EMA as of December 2004.

Method 2—Reported Number of Persons Living with HIV/AIDS or AIDS

For each state or EMA, we calculated the number of persons whose vital status was “alive” in the HIV/AIDS reporting system as of December 31, 2004. Persons whose state or EMA of residence was unknown were excluded. This total count is the estimated number of people living with AIDS in the state or EMA as of December 2004. This method was also used to calculate the number of persons reported as living with HIV/AIDS (Tables 3 and 4).

Method 3—Estimated Number of Persons Living with HIV/AIDS or AIDS

Estimated AIDS data are adjusted for reporting delays by a maximum likelihood statistical procedure; differences in reporting delays due to geographic area of residence, race/ethnicity, age, sex, vital status, and transmission categories are taken into account, but it is assumed that delays in reporting information in these categories have not changed over time. Two maximum likelihood procedures [1, 2] are performed: (1) for delays in reporting AIDS cases and (2) for delays in reporting AIDS deaths. On the basis of the results of these procedures, each AIDS case is assigned an AIDS incidence adjustment weight and an AIDS death adjustment weight. The point estimate of the number of persons living with AIDS is derived by subtracting the estimated cumulative number of deaths of persons with AIDS from the estimated cumulative number of persons with a diagnosis of AIDS. The estimates from this method are based on AIDS cases diagnosed and deaths that occurred through December 2004 and that were reported to CDC through June 30, 2005. The estimated numbers of AIDS cases and AIDS deaths are adjusted for reporting delays, but not for incomplete reporting.

This method was also used to calculate the estimated numbers of persons living with HIV/AIDS (Tables 3 and 4).

1. Green TA. Using surveillance data to monitor trends in the AIDS epidemic. Stat Med 1998:17:143–154.
2. Castillo-Chavez C, ed. Mathematical and Statistical Approaches to AIDS Epidemiology. New York: Springer-Verlag; 1989:58–88. Lecture Notes in Biomathematics 83.