Research question/goal:

The mixed-member electoral system in German Bundestag elections serves as application case for the spatial theory of party competition. This theory offers a framework to model the interdependence of voting behaviour at the micro level and party strategies at the macro level. Ideological and policy distances between voters and parties and competence attributes (valence) of parties and constituency candidates motivate party list and candidate votes. Plausible assumptions about national party motivations and district candidates’ targets allow for conclusions about competitive electoral strategies. The empirical analyses used both survey data for various federal elections and the official election results at national and constituency level.

The mixed-member electoral system differs from pure proportional systems in three respects. First, district electorates decide about constituency winners, thereby relying strongly on valence attributes of candidates. Second, the party of the district winner is able to win bonus votes from voters whose top choice options are the larger parties that are able to lead a government, so that a bonus for a district winner is equivalent to a malus for the other larger party and not for smaller parties. Third, constituency victories not simply are locally induced events but depend more than party list votes and proportional representation on the valence of national parties. From our analyses we conclude that mixed-member electoral systems tend to strengthen bipolar competition due to the first-past-the-post mechanism of district pluralities, thereby also strengthening the influence of the electorate on government formation, whereas the proportional component opens opportunities for policy offers of smaller parties.