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Primaries and Candidate Polarization: Behavioral Theory and Experimental Evidence


Do primary elections cause candidates to take extreme, polarized positions? Standard equilibrium analysis predicts full convergence to the median voter’s position with complete information, but behavioral game theory predicts divergence when players are policy-motivated and have out-of-equilibrium beliefs. Theoretically, I show that primary elections can cause greater extremism or moderation, depending on the beliefs candidates and voters have about their opponents. In a controlled incentivized experiment, I find that candidates diverge substantially and that primaries have little effect on average positions. Voters employ a strategy that weeds out candidates who are either too moderate or too extreme, which enhances ideological purity without increasing divergence. The analysis highlights the importance of behavioral assumptions in understanding the effects of electoral institutions.

Corresponding author
Jonathan Woon is a Professor, Department of Political Science, Department of Economics (secondary), and Pittsburgh Experimental Economics Laboratory, 4437 Wesley W. Posvar Hall, Pittsburgh, PA, 15260 (
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Thanks to Keith Dougherty, Sandy Gordon, Greg Huber, Scott Moser, Charlie Plott, Danielle Thomsen, Alan Wiseman, the editor and anonymous reviewers, participants at the Yale CSAP American Politics Conference, seminar participants at Washington University in St. Louis, University of Oxford (Nuffield College CESS), IC3JM (Juan March Institute), and the Pittsburgh Experimental Economics Lab for helpful comments and feedback. I am also indebted to Kris Kanthak for vigorous discussions during the early stages of this project. Previous versions of the paper were presented at the 2014 Annual Meeting of the American Political Science Association, the 2016 Public Choice Society Meeting, and the 2016 Midwest Political Science Association Conference. This research was supported by the National Science Foundation (SES-1154739) and was approved by the University of Pittsburgh Institutional Review Board under protocol PRO14060001. Replication material is available on the American Political Science Review Dataverse:

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