Geography and the Spatial Diffusion of Miranda v. Arizona in State Supreme Courts

Abstract

Diffusion studies are common in political science. Scholars have long believed that geography (or the regional effect) is one dimension of diffusion. However, the strength of the regional effect often varies among cases and has yielded inconsistent results. We employ a social learning model to examine the role of geography in the diffusion of Supreme Court precedent in state supreme courts. Previous studies of lottery diffusion demonstrate that geographic proximity to states with lotteries leads to adoption of lotteries by states. Similarly, research on citation patterns among state courts shows that states tend to cite states geographically proximate to them, as well as those who serve as precedent ‘leaders.’ State supreme court justices may learn about the applicability of Supreme Court precedent by referencing the decisions of the high courts in neighboring states. By paying attention to the decisions of their neighboring courts, state supreme court justices may reduce the uncertainty associated with the precedent, which in turn will increase the likelihood of adherence. We make use of graphical information systems (GIS) and estimate a multivariate model to better understand the diffusion of Miranda v. Arizona in state supreme courts. We find that both the ideological distance between state supreme courts and the geographic proximity of states influences the likelihood of adoption.