Modeling Regional Effects on State Policy Diffusion

Generations of state politics scholars have believed that a U.S. state is more likely to adopt a law if its neighboring states have already done so, that is, that there is a positive regional effect on policy diffusion. But rarely has the social learning process, the theoretical underpinning of this effect, been examined critically Furthermore, the statistical models used to assess this effect have been fundamentally flawed. In this article, I consider more fully the potential impacts of social learning on policy diffusion, and develop a simple approach to modeling these impacts more flexibly. Using this approach, I take a fresh look at data from two classic studies of state policy diffusion and demonstrate that the regional effect is more complex than previously believed.