Primary Elections and Partisan Polarization in the U.S. Congress

Many observers and scholars argue that primary elections contribute to ideological polarization in U.S. politics. We test this claim using congressional elections and roll call voting behavior. Many of our findings are null. We find little evidence that the introduction of primary elections, the level of primary election turnout, or the threat of primary competition are associated with partisan polarization in congressional roll call voting. We also find little evidence that extreme roll call voting records are positively associated with primary election outcomes. A positive finding is that general election competition exerts pressure toward convergence as extreme roll call voting is negatively correlated with general election outcomes. ∗ This paper is part of a project supported by National Science Foundation Grant Number SES0617556. The opinions, findings, and conclusions or recommendations expressed in this article do not necessarily reflect the views of the National Science Foundation. We thank participants at the 2008 Midwest Political Science Association Conference and David Mayhew for their helpful comments and suggestions. Shigeo Hirano thanks the Center for the Study of American Politics at Yale University for institutional and financial support. Supplementary Material available from: http://dx.doi.org/10.1561/100.00008052_supp MS submitted 15 July 2008; final version received 24 March 2010 ISSN 1554-0626; DOI 10.1561/100.00008052 © 2010 S. Hirano, J. M. Snyder Jr., S. Ansolabehere and J. M. Hansen