Simulation modelling of complex human policy issues : towards a broad interdisciplinarity

Computer simulation models are being used increasingly as decision support tools for policy-making regarding many complex human-related policy issues. It is important to know how to apply modelling to the issues appropriately, that is, to properly understand the relationship between the real situation and the model of the situation. Starting with a review of current thinking in the philosophy of (physical) science and other literatures dealing with the methodology of economics and with metaphor, the concept of a model is expanded to include the informal assumptions upon which formal structures are founded. Two types of interdisciplinarity are identified; the 'broad', which establishes dialogue between the non-formal foundations, and the 'narrow', which does not. These ideas are then applied specifically to the case of systems modelling (including system dynamics, complex systems and quasi-formal systems) of human-related issues. These debate between a mainstream and 'ecological' economics is introduced. A broad interdisciplinary reading suggests that the division between these two schools is at best useful in only some circumstances, and hides a number of other important divisions within the field. The polarisation between ecological pessimists and technological optimists is seen to have less to do with the intellectual content of the theories than with the social, ideological, personal and political context of those participating. Three case studies of policy-relevant models are introduced, both as an illustration of the practise of broad interdisciplinary thinking and as a way of advancing the debate between mainstream and ecological economics. The ECCO model represents national and regional sustainability options in the biophysical context using conventional system dynamics. The CarteSim model represents changes in spatial land-use patterns at the regional and urban level using complex system dynamics. The IPSO model is a hybrid