Quarterly Journal of Political Science, 2011, 6: 197–233 A Regression Discontinuity Test of Strategic Voting and Duverger’s Law∗ Thomas Fujiwara Department of Economics, Princeton University, USA;
[email protected]. ABSTRACT This paper uses exogenous variation in electoral rules to test the pre- dictions of strategic voting models and the causal validity of Duverger’s Law. Exploiting a regression discontinuity design in the assignment of single-ballot and dual-ballot (runoff) plurality systems in Brazilian mayoral races, the results indicate that single-ballot plurality rule causes voters to desert third placed candidates and vote for the top two vote getters. The effects are stronger in close elections and cannot be explained by differences in the number of candidates, as well as their party affiliation and observable characteristics. Political scientists and economists have long been interested in the question of whether citizens vote sincerely or strategically. How voting decisions take place is not only fundamental to the understanding of the demo- cratic process, but also has important implications for the formulation of ∗ The author would like to thank Siwan Anderson, Matilde Bombardini, Laurent Bouton, Nicole Fortin, Patrick Francois, Thomas Lemieux, Benjamin Nyblade, Francesco Trebbi, the editors, two anonymous referees, and participants at the 2009 North American and European Sum- mer Meetings of the Econometric Society for their helpful comments. Financial support from SSHRC, the Province of British Columbia, and CLSRN is gratefully acknowledged. Supplementary Material available from: http://dx.doi.org/10.1561/100.00010037 supp MS submitted 18 May 2010 ; final version received 14 September 2011 ISSN 1554-0626; DOI 10.1561/100.00010037 c 2011 T.