A multilevel time-series model for the incidence of AIDS cases in Spain.

OBJECTIVE: The main aim of this research is to study the quantitative evolution of the incidence of AIDS in the 19 Spanish Communities. The hypothesis is that incidence follows a multilevel autoregressive model, where each Community shows random variability around a general process. METHOD: On the basis of official data on the number of existing AIDS cases, an autorregressive multilevel time-series model was developed. RESULTS AND CONCLUSIONS: Analysis shows that the hypothesis is supported, indicating that overall AIDS incidence in Spain has already reached a maximum and has a tendency to remain stable or to decline in future. Long term expected values have become stable in most Communities; a slight increase is expected only in Extremadura. However, this Community has a relatively sparse population, and its contribution on the overall Spanish incidence is small. Long term expected values are estimated to be around 152.99 new cases per million inhabitants per year. This value is slightly smaller than the maximum incidence, observed in 1994 (179.4 cases).