Comparison of trends in HIV infection for two risk categories

Sensible plans for health-care needs and determination of priorities for expenditure require regular assessment of trends in HIV incidences. In particular, trends in the relative HIV incidences of different risk categories are useful when assessing whether current control strategies are working equally well for all risk categories. Here five tests for such trends are proposed for the analysis of AIDS incidence data and their performances are compared by a simulation study, assuming a log-linear trend in the HIV incidences for two risk categories. A convenient test based on a log-linear model for AIDS incidences is found both effective and robust to the nature of the underlying trend. The maximum likelihood estimate of the trend parameter is found stable even though estimates of other HIV incidence parameters are unstable. Smoothing of estimates of the other HIV incidence parameters is recommended because this dramatically reduces the rate of convergence of the iterative methods used to obtain the estimates.