In this paper we study the properties of the plurality and approval voting in the case in which the majority is divided between two alternatives as a result of information imperfections and the minority backs a third alternative, which the majority views as strictly inferior. The majority thus faces two problems: aggregating information and coordinating to defeat the minority candidate. We show that under plurality voters have to concentrate all their strength in fighting one of this problems. With approval voting instead, voters can face both problems simultaneously. We then test the pivotal voter model in the lab, and we observe that most predictions are indeed satisfied. Under plurality we only find evidence of Duverger’s Law under the threat of a large minority. Under approval voting, majority voters double vote less than predicted but, still, double-voting increases with the size of the minority. Finally, approval voting performs very well from a welfare viewpoint, and vastly outperforms plurality.
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