How it works
The two-round system aims to ensure that the winner has majority support. Voters choose their favorite in the first round and choose among the remaining candidates in the second. Shugart and Carey (1992) noted that many presidential systems adopted it to elect legitimate presidents. Because runoffs do not always select the Condorcet winner, they are often compared with approval voting (Fishburn & Brams, 1981).
Duverger's hypothesis
Duverger (1954) argued that plurality rule produces two-party systems while runoffs produce multiparty systems, because wasted-vote concerns are weaker in the first round and voters can vote sincerely. This is the companion to Duverger's law. Exploiting a population threshold in Brazil, Fujiwara (2011) gave causal evidence that third-place and lower candidates gain votes in cities with runoffs.
Strategic voting and assessments
Bouton (2013) and Bouton and Gratton (2015) showed that voters in runoffs may still vote strategically, trying to end the race in the first round or shape who reaches the runoff, so Duverger's hypothesis does not always hold. Pons and Tricaud (2018) showed that when three candidates remain in French legislative runoffs, expressive voting for preferred candidates can change outcomes.
FAQ
- What is the two-round system in simple terms?
- If nobody gets more than half the votes in the first round, voters choose again between the top finishers.
- Why is it linked to multiparty systems?
- In the first round voters worry less about wasting their vote, so they feel free to support small-party candidates.
Sources reviewed: 2026-10-26
References
- Duverger, M. (1954). Political parties: Their organization and activity in the modern state. Methuen. Duverger's hypothesis on runoffs.
- Bouton, L. (2013). A theory of strategic voting in runoff elections. American Economic Review, 103(4), 1248–1288. Strategic voting in runoffs.
- Bouton, L., & Gratton, G. (2015). Majority runoff elections: Strategic voting and Duverger's hypothesis. Theoretical Economics, 10(2), 283–314. Revisiting Duverger's hypothesis.
- Fujiwara, T. (2011). A regression discontinuity test of strategic voting and Duverger's law. Quarterly Journal of Political Science, 6(3–4), 197–233. Causal evidence from Brazil.
- Pons, V., & Tricaud, C. (2018). Expressive voting and its cost: Evidence from runoffs with two or three candidates. Econometrica, 86(5), 1621–1649. Expressive voting in French runoffs.
- Shugart, M. S., & Carey, J. M. (1992). Presidents and assemblies: Constitutional design and electoral dynamics. Cambridge University Press. Runoffs in presidential systems.
- Fishburn, P. C., & Brams, S. J. (1981). Approval voting, Condorcet's principle, and runoff elections. Public Choice, 36(1), 89–114. Runoffs versus approval voting.