A Rational Calculus of Voting Considering Coalition Signals: The 2005 German Bundestag Election as an Example

This article extends the calculus of rational voting (Riker & Ordeshook, 1968) by considering the coalition building process and the legislative process (cf. Austen-Smith & Banks, 1988) in multi-party systems. Comparing preferences on coalitions and their resulting legislative outcomes instead of party preferences, I create preference profiles of voters on coalitions and estimate the probability that a coalition forms, given the parties' coalition signals, and an expected electoral result. I illustrate the results of this rational calculus for the German Bundestag elections 2005 as a political map. Furthermore, this calculus allows the identification of coalition signals which raise and reduce a party's vote share.