Abstract

This article conducts a decision theoretic analysis of the effect of dual candidacy on voting decisions in the Japanese variant of the mixed electoral system, where each candidate can run in both a single-member district (SMD) and a proportional representation (PR) block, and dual candidates can be ranked either individually or equally in parties' PR lists: their post-election ranking is determined by their SMD votes. The model shows that dual candidacy differentiates the mixed system from merely the simultaneous use of the SMD and PR systems. That is, if an SMD candidate also runs in the PR block, it lowers voters' utility increment obtained by casting their SMD votes for him. If he is ranked equally in the PR list, however, SMD votes for him may help him win a PR seat against other equally ranked dual candidates, which enables dual candidacy accompanied by equal ranking to attract more SMD votes