A meta-analysis of estimates of the AIDS incubation distribution.

Information from 12 studies is combined to estimate the AIDS incubation distribution with greater precision than is possible from a single study. The analysis uses a hierarchy of parametric models based on a four-parameter generalized F distribution. This general model contains four standard two-parameter distributions as special cases. The cases are the Weibull, gamma, log-logistic, lognormal distributions. These four special cases subsume three distinct asymptotic hazard behaviors. As time increases beyond the median of approximately 10 years, the hazard can increase to infinity (Weibull), can plateau at some constant level (gamma), or can decrease to zero (log-logistic and lognormal). The Weibull, gamma and 'log-logistic distributions' which represent the three distinct asymptotic hazard behaviors, all fit the data as well as the generalized F distribution at the 25 percent significance level. Hence, we conclude that incubation data is still too limited to ascertain the specific hazard assumption that should be utilized in studies of the AIDS epidemic. Accordingly, efforts to model the AIDS epidemic (e.g., back-calculation approaches) should allow the incubation distribution to take several forms to adequately represent HIV estimation uncertainty. It is recommended that, at a minimum, the specific Weibull, gamma and log-logistic distributions estimated in this meta-analysis should all be used in modeling the AIDS epidemic, to reflect this uncertainty.

The assumption of no long reporting delays may result in underestimates of US AIDS incidence.

OBJECTIVE: To evaluate the effect of the assumption of no long reporting delays on estimates of AIDS incidence. DESIGN: Reported AIDS cases must be adjusted for reporting delays to estimate AIDS incidence. We compared the adjustments supplied with the Centers for Disease Control and Prevention (CDC) AIDS Public Information Data Set with a set of adjustments that differ with respect to CDC assumption of no long delays. Both methods assume that no changes in delay have occurred throughout the reporting period. METHODS: Probability distributions of reporting delays were calculated from the delay adjustment weights supplied by CDC, and from an alternative method that estimates the probability of long delays from the surveillance data. AIDS incidence estimates from these two approaches were calculated and compared. RESULTS: The CDC adjustments assume that there will be no reporting delays longer than 61 months, whereas the alternative method estimates that 5.9% of case reports will be delayed longer than 61 months. The CDC adjustments result in lower estimates of AIDS incidence and a flattening of the epidemic. CONCLUSIONS: In addition to a 6.2% reduction in total estimated AIDS incidence, the CDC assumption changes the shape of the estimated epidemic. These may result in as much as 4-21% reductions in model estimates of HIV incidence and prevalence.

Populations at increased risk of HIV infection: current knowledge and limitations.

Research data describing the prevalence and patterns of behaviors that place persons at increased risk of HIV infection are extremely limited. The scarcity of data has constrained potential applications of surveillance data, research on specific high-risk behaviors, and epidemiological studies. This article critically reviews available research for four population groups: intravenous drug users, homosexual males, and sexually active adolescents and adults. The fallacies inherent in estimating risk group size underscore the need for population-based research that can provide detailed data on sexual and drug use behaviors.

Determinants of contraceptive switching behavior in rural Sri Lanka.

This study examines the influence of a selected set of determinants of contraceptive method switching in rural Sri Lanka. Of interest is the question of how change in contraceptive practice at the individual level can account for patterns observed at the aggregate level. Based on calendar data on contraceptive use over a 3-year period, collected for more than 3,000 married women in a 1986 survey, the multivariate analysis shows that women who attain all or a significant proportion of their desired fertility tend to switch to more effective methods. Women who experience method failure tend to switch methods, usually to a type that is more effective. The woman's background determinants of age and education have small but significant effects on method switching, whereas the effect of household economic well-being is not significant. There is strong indication that rural couples are practicing contraception in a nonrandom fashion, switching methods in accordance with changes in their fertility motivations and contraceptive experience.