Ideological trends and changing party system polarization in western democracies

Abstract

Party system polarization has large effects on individual behaviour and on election consequences. For example, when the large parties are close to the median voter, any outcome creates congruent governments. When they diverge, governments are usually much further away. However, we know surprisingly little about the causes of party system polarization. This paper explores the relative influences and relationships between international ideological trends, domestic voter diversity and party system left-right polarization in Western democracies. Citizen self-placement data from the Eurobarometer, World Value and CSES studies, and party position data from the comparative manifesto project and CSES, are used to analyse these dynamic movements and their consequences from the mid-1970s through 2005.