Measuring and comparing party ideology and heterogeneity

Estimates of party ideological positions in Western Democracies yield useful party-level information, but generally lack the ability to provide an insight into the intraparty politics of party elites. In this article, we generate comparable measures of latent individual policy positions from elite survey data that enable analysis of elite-level party ideology and heterogeneity. This approach has some advantages over both expert surveys and approaches based on behavioral data, such as roll-call voting, and is directly relevant to the study of party cohesion. We generate a measure of elite positions for several mostly European countries using a common space scaling approach and demonstrate its validity as a measure of party ideology. We then apply these data to examine sources of party elite heterogeneity, focusing on the role of intraparty competition in electoral systems, nomination rules, and party goals. We find that policy-seeking parties and centralized party nomination rules are associated with less party heterogeneity. While intraparty competition has no effect, such contexts appear to condition the effect of district magnitude.