Public Opinion Quarterly Advance Access originally published online on May 21, 2008
Public Opinion Quarterly 2008 72(2):216-240; doi:10.1093/poq/nfn018
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Estimating Causal Effects of Ballot Order from a Randomized Natural Experiment
The California Alphabet Lottery, 1978–2002
Address correspondence to Daniel E. Ho (e-mail: dho{at}law.stanford.edu) or Kosuke Imai (e-mail: kimai{at}princeton.edu).
Randomized natural experiments provide social scientists with rare opportunities to draw credible causal inferences in real-world settings. We capitalize on such a unique experiment to examine how the name order of candidates on ballots affects election outcomes. Since 1975, California has randomized the ballot order for statewide offices with a complex alphabet lottery. Adapting statistical techniques to this lottery and addressing methodological problems of conventional approaches, our analysis of statewide elections from 1978 to 2002 reveals that, in general elections, ballot order significantly impacts only minor party candidates, with no detectable effects on major party candidates. These results contradict previous research, finding large effects in general elections for major party candidates. In primaries, however, we show that being listed first benefits everyone. Major party candidates generally gain one to three percentage points, while minor party candidates may double their vote shares. In all elections, the largest effects are for nonpartisan races, where candidates in first position gain three percentage points.
DANIEL E. HO is with the Stanford Law School, 559 Nathan Abbott Way, Stanford CA 94305, USA. KOSUKE IMAI is with the Department of Politics, Princeton University, Princeton NJ 08544, USA. An earlier version of this article is available as Ho and Imai (2004). We thank the editor, four anonymous referees, Jim Alt, Ian Ayres, Larry Bartels, Barry Burden, Jamie Druckman, Marty Gilens, Brian Jacob, Dale Jorgenson, Gary King, Al Klevorick, Jon Krosnick, Hanna Lee, John Londregan, Becky Morton, Kevin Quinn, Donald Rubin, Jas Sekhon, Sarah Sled, Jim Stock, Liz Stuart, and Stephen F. Williams for helpful comments. Joe Falencki, Claudia Ornelas, and Tim Shapiro provided excellent research assistance. We are also grateful to Janice Atkinson at the Sonoma County Registrar of Voters, Gail Pellerin at the Santa Cruz County Registrar of Voters, Genevieve Troka at the California State Archives, and Karin MacDonald of the California Statewide Data Base at the University of California, Berkeley for their kind and resourceful help in collecting California's randomized alphabets, election returns, and registration data. Finally, we thank seminar participants at Harvard University, Princeton University, and Yale Law School for stimulating discussions.
Research support was provided in part by the National Science Foundation (SES–0550873), the Committee on Research in the Humanities and Social Sciences at Princeton University, the Institute for Quantitative Social Science, the Project on Justice, Welfare and Economics, and the Center for American Political Studies at Harvard University, and the Center for Law, Economics, and Organization at Yale Law School.