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Abstract
This article builds on the recent policy diffusion literature and attempts to overcome one
of its major problems, namely the lack of a coherent theoretical framework. The literature
defines policy diffusion as a process where policy choices are interdependent, and
identifies several diffusion mechanisms that specify the link between the policy choices of
the various actors. Since these mechanisms are grounded on different theories, theoretical
accounts of diffusion have currently little internal coherence. In this article we put forward
an expected-utility model of policy change that is able to subsume all diffusion
mechanisms. We argue that the expected utility of a policy depends on both its
effectiveness and the payoffs it yields, and we show that the various diffusion mechanisms
operate by altering these two parameters. Each mechanism affects one of the two
parameters, and does so in distinctive ways. To account for aggregate patterns of
diffusion, we embed our model in a simple threshold model of diffusion. Given the high
complexity of the process that results, strong analytical conclusions on aggregate patterns
cannot be drawn without more extensive analysis that is beyond the scope of this paper,
but preliminary considerations indicate that a wide range of diffusion processes may exist
and that convergence is only one possible outcome.
Convention