User interfaces, population generators, stochastic state transitions, discrete time processing, and outcome analyzers support the modeling efforts and display results. Software systems using special sampling methods help analyze the sensitivity of the results to changes in model features and values. Stochastic micropopulation models allow a variety of hypotheses to be modeled about etiology, spread, ascertainment and control of disease. In addition, it is possible to study the effects of random variability in population structure, behavior and disease development. The software is provided free of charge.
Individuals contact one another in mixing groups or through a network of partnerships.
Stages of infection can include latent and incubation periods, expression of symptoms, withdrawal from some types of contacts, and immunity. The effects of assumed durations and degrees of infectiousness at these stages may be examined. Public health measures and the effects of behavioral changes are studied by varying contact rates and other model parameters. A specialization of the infectious disease component resulted in aseries of integrated models simulating HIV transmission, AIDS progression and disease-associated care. Recent studies have examined rates of disease in intravenous drug using communities, with separate states for drug recruitment, addiction, treatment and incarceration.