Party Competition and Conflict in State Legislatures

This article examines the relationship between party competition for control of governing institutions and legislative party polarization. Although the competition/cohesion thesis dates to the 1940s, it has never before been subject to a test with data from the 50 states. Drawing upon newly available data, we take stock of the evidence. Five measures of party competition are used: (1) the number of recent shifts of party control, (2) an index of party competition for state offices, (3) the closeness of presidential elections in the state, (4) the effective number of political parties in the state, and (5) the ratio of Republicans to Democrats in the electorate. Nearly all of these measures correlate with higher levels of party polarization in both the lower and upper chambers, and none are associated with a lower level of polarization.