Party System Polarization and the Ideological Congruence: Causal Mechanisms (Updated).

The ideological congruence between the median citizen and the government is shaped by various institutional features, especially the party system. The polarization of the party system has large and robust effects on ideological (in)congruence across a variety of political systems. As captured by several approaches to measuring congruence, and across a substantial span of time, more polarization makes it more difficult to form congruent governments in parliamentary democracies. This paper focuses on the process of parliamentary government formation as the causal linkage between polarization and congruence. The analysis supports our expectation that polarization works somewhat differently under the different election rules. In the PR systems we find polarization shaping congruence through its association with greater distances of the plurality or preelection coalition plurality vote winner, but also through the distances of the legislative median party, the previous government, and even the runner-up plurality party. In the SMD systems the effects are entirely through the plurality (or pre-election coalition plurality) vote winner. New data from CSES Module 3 and from the Manifesto project make it possible to analyze the two data sources in parallel and compare similarities and differences in polarization and its processes. [ABSTRACT FROM AUTHOR]