A role for system dynamics in modelling the spread of AIDS

System dynamics has a role to play in modelling the spread of infectious diseases. Its utility for this purpose is illustrated through a model of the spread of AIDS in the homosexual population of the UK. By virtue of its constituent diagramming tools, style of equation formulation and special-purpose computer software, system dynamics offers a means of rendering epidemiological models more transparent to the client than many of the mathematical models published to date. In respect of the AIDS spread model, the relative ease of adding (i) a heterogeneous sexual-activity profile, and (ii) a variable infectivity profile onto a base model, is described. Finally, results are reported from an optimisation experiment applied to the most complex model. The ‘best fit’ obtained allows an estimate of the (unknown) HIV population to be made.