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The Effect of the Top Two Primary on the Number of Primary Candidates


  • Kevin Henrickson shall share all data and coding for replication purposes. We are extremely appreciative of the insightful comments that we received on this article at both the 2010 Public Choice Society Annual Meetings and the 2010 Midwest Economic Association Annual Meetings.

Direct all correspondence to Kevin Henrickson, Department of Economics, Gonzaga University, 502 E. Boone Ave., Spokane WA 99528; e-mail:



Washington State held its first “top two primary” in 2008. Under this system, the two candidates receiving the most votes move on to the general election, regardless of party affiliation. This study empirically examines the potential incentive under this top two primary system for each political party to discourage “excess” party candidates from entering primary contests.


We examine this possibility by looking at the Washington State Legislative Primaries in 2004, 2006, 2008, and 2010. With these data, we estimate the factors impacting the number of primary candidates in a race for each political party, including the change in the primary format in 2008.


Our results indicate that the switch to the top two primary reduced the likelihood of having multiple Democratic candidates in a race, reduced the number of “excess” Democratic candidates, but did not have a significant impact on Republican candidates.


With many states revising their primary systems, an understanding of the incentives present under alternative systems is critical. As such, the results presented in this study provide evidence that the top two primary gives the political parties an incentive to discourage excess primary candidates.