Jacob Montgomery - Ends Against the Middle: Scaling Votes when Ideological Opposites Behave the Same for Antithetical Reasons
Jacob Montgomery, Associate Professor of Political Science, Washington University in St. Louis
Standard methods for measuring ideology from voting records assume strict monotonicity of responses in individuals’ latent traits. If this assumption holds, we should rarely observe instances where individuals at the ideological ends vote together in opposition to moderates. In practice, however, there are many times when individuals from both extremes vote identically but for opposing reasons. For example, both liberal and conservative justices may dissent from the same Supreme Court decision but provide ideologically contradictory rationales. In legislative settings, ideological opposites may join together to oppose moderate legislation in pursuit of antithetical goals. In this paper, we introduce a scaling model that accommodates non-monotonic response functions and provide a novel estimation approach that improves upon existing routines. We apply this method to voting data from the U.S. Supreme Court and Congress and show that it outperforms standard methods in terms of both model fit and substantive insights. We argue that our proposed method represents a superior default approach for generating one-dimensional ideological estimates in many important settings of interest to political science.
Jacob Montgomery is an Associate Professor in the Department of Political Science at Washington University in St. Louis. His research is in the areas of political methodology and American politics, with a special interest in political parties. He teaches courses on statistical methods and American political parties.