Proportional Representation and Strategic Voters

The goal of this paper is to examine the incentives to vote insincerely, other than those created by rounding, faced by voters in systems of proportional representation (PR). We rigorously investigate two models of voter behaviour. The first model assumes that a voter is primarily interested in the distribution of seats in the post-election parliament (seat maximizer) while the second considers a voter who is concerned with the distribution of power in it (power maximizer). We show that under pure PR, seat maximizers do not have any incentives to manipulate, which justifies the Bowler and Lanoue (1992) claim, and that such incentives for seat maximizers appear with the introduction of a threshold. We show that, even in the absence of a threshold, there will always exist circumstances where a power maximizer would have an incentive to vote insincerely. We demonstrate that her incentives to make an insincere vote depend on her attitude towards uncertainty. The introduction of a threshold creates new and stronger opportunities for strategic voters regardless of their attitude towards uncertainty. Finally we discuss the overshooting/undershooting phenomenon, when either too many or too few like-minded voters attempt to manipulate. We use the two models to explain voters’ behaviour at the 2005 New Zealand general election and demonstrate that rounding creates not only incentives but also disincentives for strategic voting.