Nils D. Steiner, Matthias Mader
Intra-Party Heterogeneity in Policy Preferences and Its Effect on Issue Salience: Developing and Applying a Measure Based on Elite Survey Data

Party Politics, 2019: 25, issue 3, pp. 336–348
ISSN: 1354-0688 (print); 1460-3683 (online)

Quantitative research on party politics often has to assume that parties are unitary actors with homogeneous policy preferences simply because intra-party heterogeneity is difficult to measure. This article proposes a measure of preference heterogeneity based on surveys of party elites. We draw on Comparative Candidates Survey (CCS) data from 28 elections in 21 developed democracies to quantify intra-party heterogeneity and validate this measure. The usefulness of the measure is demonstrated by studying the effects of intra-party heterogeneity on issue salience. We find support for the hypothesis that heterogeneity regarding a policy issue tends to be negatively associated with the emphasis a party places on that issue by regressing measures of issue salience from the Chapel Hill Expert Survey and the Manifesto Project on our CCS measure of heterogeneity. Problems of elite surveys notwithstanding, drawing on this data source seems a promising way to overcome the unitary party assumption.