Abstract
Experience in using a mathematical model in the strategic planning of Health and Personal Social Services (HPSS) suggests some lessons that may be relevant to strategic modelling in other public services. Two attributes of the HPSS are that its final outputs cannot be measured reliably and that it is organized hierarchically with field authorities having considerable autonomy from the central authority. A model that has proved useful in this situation simulates how the field authorities respond to decisions taken at the centre on aggregate resource availabilities and describes their responses in terms of intermediate or proxy measures of service output. The model is used interactively with planners to examine policy options. It takes account of ideal patterns of service delivery, not merely current practice, and of the priorities and preferences employed by service personnel in the field.