Polls, coalitions and strategic voting under proportional representation

How do polls influence strategic voting under proportional representation? This paper derives a strategic calculus of voting for coalitions that generates testable predictions about the effects of polls on strategic voting in elections involving four or more parties. Incentives of leftist voters to vote for a centrist over a noncentrist party are shown to increase with the difference in expected seats between the prospective right-wing and left-wing coalitions (and vice versa for rightist voters). Centrist voters’ incentives to vote for a center-left vs a center-right party are also shown to depend on the relative strengths of the right-wing and left-wing coalitions. Importantly, the strategic voting incentives studied here do not depend on the presence of electoral thresholds or other features of the electoral system. The predictions are tested with survey data from parliamentary elections in Austria and Germany.