Abstract

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.

Related Papers

Blackwell, Matthew, Jacob R. Brown, Sophie Hill, Kosuke Imai, and Teppei Yamamoto (2025). ``Priming bias versus post-treatment bias in experimental designs.'' Political Analysis, Vol. 33, No. 4 (October), pp. 361-377. Winner of Political Analysis Editors' Choice Award.

Goplerud, Max, Kosuke Imai, Nicole E. Pashley (2025). ``Estimating Heterogeneous Causal Effects of High-Dimensional Treatments: Application to Conjoint Analysis.'' Annals of Applied Statistics, Vol. 19, No. 2 (June), pp. 866-888.

Ham, Dae Woong, Kosuke Imai, and Lucas Janson (2024). ``Using Machine Learning to Test Causal Hypotheses in Conjoint Analysis.'' Political Analysis, Vol. 32, No. 3 (July), pp. 329-344.

Johnson, Rebecca A., Tyler Simko, and Kosuke Imai (2024). ``A Summer Bridge Program for First-Generation Low-Income Students Stretches Academic Ambitions with No Adverse Impacts on GPA.'' Proceedings of the National Academy of Sciences, Vol. 121, No. 50, e2404924121.

de la Cuesta, Brandon, Naoki Egami, and Kosuke Imai (2022). ``Improving the External Validity of Conjoint Analysis: The Essential Role of Profile Distribution.'' Political Analysis, Vol. 30, No. 1 (January), pp. 19-45.

Egami, Naoki, and Kosuke Imai (2019). ``Causal Interaction in Factorial Experiments: Application to Conjoint Analysis.'' Journal of the American Statistical Association, Vol. 114, No. 526 (June), pp. 529-540.

Imai, Kosuke, and Zhichao Jiang (2018). ``A Sensitivity Analysis for Missing Outcomes Due to Truncation-by-Death under the Matched-Pairs Design.'' Statistics in Medicine, Vol. 37, No. 20 (September), pp. 2907-2922.

Imai, Kosuke, Dustin Tingley, and Teppei Yamamoto (2013). ``Experimental Designs for Identifying Causal Mechanisms.'' (with discussions) Journal of the Royal Statistical Society, Series A (Statistics in Society), Vol. 176, No. 1 (January), pp. 5-51. Read before the Royal Statistical Society in March, 2012.

Imai, Kosuke, and Teppei Yamamoto (2010). ``Causal Inference with Differential Measurement Error: Nonparametric Identification and Sensitivity Analysis.'' American Journal of Political Science, Vol. 54, No. 2 (April), pp. 543-560.

Imai, Kosuke (2009). ``Statistical Analysis of Randomized Experiments with Nonignorable Missing Binary Outcomes: An Application to a Voting Experiment.'' Journal of the Royal Statistical Society, Series C (Applied Statistics), Vol. 58, No. 1 (February), pp. 83-104.

Imai, Kosuke (2008). ``Sharp Bounds on the Causal Effects in Randomized Experiments with ``Truncation-by-Death.'' Statistics & Probability Letters, Vol. 78, No. 2 (February), pp. 144-149.

Horiuchi, Yusaku, Kosuke Imai, and Naoko Taniguchi (2007). ``Designing and Analyzing Randomized Experiments: Application to a Japanese Election Survey Experiment.'' American Journal of Political Science, Vol. 51, No. 3 (July), pp. 669-687.

Ho, Daniel E., and Kosuke Imai (2006). ``Randomization Inference with Natural Experiments: An Analysis of Ballot Effects in the 2003 California Recall Election.'' Journal of the American Statistical Association, Vol. 101, No. 475 (September), pp. 888-900.