The Evolution of Partisan Conventions

This paper models partisanship and nonpartisanship as alternative norms or conventions of behavior. Evolutionary game theoretic techniques are used to analyze the selection of partisanship or nonpartisanship by a population inter-acting over time. Equilibrium selection in the model is driven by the varying observability of partisan behavior introduced by electoral institutions, coupled with the inverse relationship between the observability of partisan actions, and that of nonpartisan inactions. The model suggests that institutions which in-crease the observability of partisan actions also increase the likelihood that those actions will be taken. Conversely, institutions which decrease the observability of partisan actions thereby decrease the likelihood that such actions will be taken. We test the theoretical results from our model on aggregate levels of split ticket voting across states in the U.S. between 1880 and 1940. We find considerable support for the model in time series cross section (TSCS) estimates of the effects of electoral institutions on levels of partisanship across states, support which is undiminished after corrections for endogeneity and selection bias.