Abstract
This thesis inquires into how models are used to inform policy making and what makes models useful to those informing policy. A model is considered a formal representation of a target system that can be used to answer questions about that target system. Moreover, it is defined as the computer implementation of a mental model or conceptual model, written in algorithms or equations. This research draws on insights from existing literature on policy making, policy analysis, models and model use, which are then used to develop an analytical framework founded on science and technology studies. This framework is employed to guide an empirical investigation of models that have been used to inform policy making. Fieldwork was conducted over a period of two years at government departments, private companies and research institutes in the United Kingdom and the Netherlands. This fieldwork consisted of 38 interviews with model users, observations of model use and archival research. The data were analysed using a thematic coding approach centered on the identification of practices, intra-case and inter-case comparison. It is shown that there are similarities in how models are used and made useful by their users. More specifically, users engage in activities to (1) determine the scope of the model, (2) improve its credibility, (3) make it transparent, and (4) make it relevant. The original contribution to knowledge of this thesis consists of an in-depth description of the social context of model use and the four sets of model use practices. Moreover, it presents an analysis of how model use is facilitated and constrained by the (inter)-organisational structure of use, by model user roles, and model user communities. The thesis concludes that the usefulness of models cannot be understood in isolation from the social context; those developing models for policy would do well to consider it.