Party System Change, Election Rules and Ideological Congruence.

Ideological congruence between median voter and the government changes substantially from one decade to the next, especially in the SMD systems of Western democracies. These changes are closely linked to changing levels of party system polarization. When the large parties are close to the median voter, any outcome creates congruent governments. When they diverge, governments are usually much further away. In the PR systems, too, some depolarization of the party system contributes to greater ideological congruence, although the connections are more complex, and cross-system differences are more diverse than in the SMD systems. This paper describes the changing levels of party system polarization from 1946 through 2003, explicating the positions of political party families and tracing the implications for ideological congruence. Under conditions of relative ideological consensus, whether of leftist or center-right orientation, there is little difference in the congruence levels of SMD and PR electoral systems. The most recent decade seems to be such a period. ..PAT.-Unpublished Manuscript [ABSTRACT FROM AUTHOR]