American Political Science Review

Research Article

Making Outsiders' Votes Count: Detecting Electoral Fraud through a Natural Experiment


a1 Gakushuin University

a2 Australian National University


Weak electoral registration requirements are commonly thought to encourage electoral participation, but may also promote electoral fraud. As one possibility, candidates and their supporters can more easily mobilize voters who do not reside within the district to register there fraudulently and vote for that district's candidates. We statistically detect this classic type of electoral fraud for the first time, by taking advantage of a natural experimental setting in Japanese municipal elections. We argue that whether or not a municipal election was held in April 2003 can be regarded as an “as-if” randomly assigned treatment. A differences-in-differences analysis of municipality–month panel data shows that the increase in the new population just prior to April 2003 is significantly larger in treatment municipalities (with an election) than in control ones (without an election). The estimated effects are decisive enough to change the electoral results when the election is competitive. We argue that our approach—“election timing as treatment”—can be applied to investigate not only this type of electoral fraud but also electoral connections in other countries.


c1 Kentaro Fukumoto is Professor, Department of Political Science, Gakushuin University, 1-5-1 Mejiro, Toshima, Tokyo 171-8588, Japan (

c2 Yusaku Horiuchi is Associate Professor, Crawford School of Economics and Government, College of Asia and the Pacific, Australian National University, J.G. Crawford Building, No. 132, Canberra, ACT 0200, Australia (


Earlier versions of this article were presented at the 2009 Annual Summer Meeting of the Society of Political Methodology at Yale University and the UCLA Workshop on Japan's Post-bubble Political Economy of 2009. We thank the National Diet Library of Japan, the Japan Research Institute for Local Government, Ryota Natori, Jun Saito, and Jun'ichiro Wada for archival help; Futoshi Ueki for research assistance; and Alison Cumming Thom, Olle Folke, Shigeo Hirano, Karen Long Jusko, Andrew Leigh, Matthew Linley, Sherry Martin, Jacob Michael Montgomery, Costas Panagopoulos, Dan Smith, Rob Weiner, Atsushi Yoshida, other participants in these meetings, and the co-editor and reviewers of this journal for useful comments. Fukumoto also appreciates the financial assistance of the Gakushuin's Abe Yoshishige Memorial Educational Fund, the Gakushuin University's Computer Centre, the Inamori Foundation, the Japan Society for the Promotion of Science [Grant-in-Aid for Scientific Research (B) 20330023], and the Joint Usage/Research Center (2008–2012; Ministry of Education, Culture, Sports, Science and Technology, Japan).