How Divisive Primaries Hurt Parties: Evidence from Near-Runoffs

33 Pages Posted: 5 May 2016

See all articles by Alexander Fouirnaies

Alexander Fouirnaies

Harris School at University of Chicago

Andrew Hall

Stanford University

Date Written: May 4, 2016


In many democracies, parties and their voters rely on competitive primary elections to choose nominees for the general election. Competitive primaries may help parties select higher quality candidates and advertise these candidates to voters, but they also run the risk of exposing nominees' flaws, offending losing candidates' supporters, and making the party look weak to general-election voters. Do longer, more competitive primaries help or harm parties in the general election? The existing literature on so-called divisive primaries comes to mixed conclusions, likely because of chronic issues of omitted variable bias and reverse causation. In this paper, we address these problems by taking advantage of U.S. states that use runoff primaries, second-round elections which, when triggered, create longer, more contentious primaries. Using a regression discontinuity design in primary elections close to the runoff threshold, we find large and negative effects of runoffs on the party's general-election fortune in the U.S. House and Senate. We estimate that going to a runoff decreases the party's general election vote share by 6-9 percentage points, on average, and decreases the probability that the party wins the general election by roughly 21 percentage points, on average. In U.S. state legislatures, in contrast, runoff primaries do not hurt, and in competitive contexts may in fact help, parties in the general election. The results suggest that divisive primary elections are highly damaging when salience is high but beneficial when salience is low, a pattern we argue is driven by the opposing effects of information in high vs. low salience primary elections.

Suggested Citation

Fouirnaies, Alexander and Hall, Andrew, How Divisive Primaries Hurt Parties: Evidence from Near-Runoffs (May 4, 2016). Available at SSRN: or

Alexander Fouirnaies

Harris School at University of Chicago ( email )

Harris School of Public Policy
1155 E 60th St
Chicago, IL 60637
United States
+17732942341 (Phone)


Andrew Hall (Contact Author)

Stanford University ( email )

Stanford, CA 94305
United States

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