Large-scale models for policy decisions

The subject of large-scale modeling has always been one of great controversy. Recently there appears to be both an increase in the call from the user community for such tools, and writing on business of difficulties associated with producing them. This article is an attempt to investigate the feasibility of producing such models. It is a summary of a forthcoming book on the same subject. It looks at them from the point of view of data, theory, implementation, validation, transfer, and use. The studies discussed are generally ones produced by EPA or NSF over the last two years. In the main: the outstanding problem area appears not to be technical but in the field of transfer and use.