Gerrymandering Opposition: Minority-Concentrated Districts and Electoral Competition in Mexico


Can institutions that are designed to improve minority representation also have an effect on electoral competition? We address this question by examining how minority-concentrated districts (MCDs)—designed to empower indigenous populations—affected minority participation and party competition in Mexico. Using an original dataset and a matching design that helps alleviate causal inference problems inherent to observational studies, we find that MCDs had no effect on minority participation but enhanced electoral competition. Field-research reveals that MCDs weakened one-party dominance by assembling minority voting blocs that were amenable to opposition-party appeals. More broadly, our results suggest that the mobilization of minority voting blocs can promote electoral competition in transitional democracies.

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  1. 1.

    We use the term minority-concentrated districts (MCDs) rather than the more conventional majority-minority districts because we adopt the Mexican government’s threshold for such a district, which is that at least 40 % of its inhabitants are ethnic minorities.

  2. 2.

    Cameron, Epstein, and O’Halloran (1996) point out that this concentration of minority voters also reduces overall support for legislation that advances minority interests.

  3. 3.

    These include all eleven states with MCDs plus eight states that do not have MCDs. The resulting dataset has 2048 municipalities out of a total of 2457 in Mexico.

  4. 4.

    Given that the average population of districts is over 325,000 inhabitants, only highly urban municipalities compose their own districts or are split into multiple districts. None of these urban municipalities have sizable indigenous populations and these are thus excluded from the analysis.

  5. 5.

    We chose to analyze midterm elections for two reasons: first, the 2009 midterm election was 4 years after the 2005 redistricting, allowing more time for this treatment to take hold than the 2006 election; second, we expect midterm elections to better reflect the response of voters to their districts’ composition than presidential elections, where coattail effects of the presidential race may play a larger role.

  6. 6.

    The prohibition of reelection in Mexico lessens the risk that our results are confounded by an incumbency effect of the type described by Hayes and McKee (2009).

  7. 7.

    In our main dataset, the PRI received the most votes in 88 % of the municipalities in 2003 and 85 % of the municipalities in 2009. In 2003, the PRI received the second-most votes in all municipalities for which it was not the top vote getter and only failed to receive the first or second-most votes in two municipalities in 2009.

  8. 8.

    Three of these 19 party representatives were appointed by the PRI, and two were appointed by the Partido Verde Ecologista de México (PVEM), a party that often runs in coalition with the PRI. The remaining 14 seats were split among parties that typically oppose the PRI, including three from the PAN, four from the PRD, four from the Partido de Trabajo (PT), and three from Convergencia (IFE 2005b, pp. 136–367).

  9. 9.

    Unfortunately, the details of these requests were not made publicly available. However, an analysis of the 2015 redistricting episode reports that all parties suggested modifications to the scenario generated by the automated algorithm and that 111 out of 544 (20 %) were adopted (Trelles, Altman, Magar, and McDonald 2015).

  10. 10.

    Genetic matching is an evolutionary search algorithm that achieves optimal “balance” on covariates between treatment and control units using observational data. It has been shown to outperform other matching techniques such as propensity-score matching (Sekhon 2011).

  11. 11.

    See Appendix B for a complete list of formal redistricting criteria. Several of these were unlikely to introduce bias and thus not included in the matching algorithm.

  12. 12.

    These 246 municipalities exclude 12 treatment units that were dropped through the use of a caliper because satisfactory matching control units could not be found. The caliper was implemented to improve balance on municipal percent indigenous, the percentage indigenous of the old district, and percent new neighbors.

  13. 13.

    As a robustness check, we tested the effect of MCDs on the effective number of parties, using the Laakso-Taagepera (1979) measure. The estimated effect was positive, but not significant, likely due to the fact that the congressional elections observed continued to be largely two-party races, albeit with narrower vote margins.

  14. 14.

    We also observe greater vote shares for the PRI and lower turnout for mestizo voters reassigned to MCDs than mestizo voters in control municipalities, suggesting that this treatment demobilized this group and caused it to support opposition parties less.

  15. 15.

    We also implemented an original field-research based EI technique, described in greater detail in Meng and Palmer-Rubin (2012).

  16. 16.

    The organization that spearheaded the Zapatista rebellion, the Ejercito Zapatista de Liberación Nacional (National Zapatista Liberation Army) withheld from forming party alliances.

  17. 17.

    Analysis by Sonnleitner (2012b, pp. 91–115) shows that indigenous nominations to the federal Chamber of Deputies increased significantly following the redistricting. In the two federal elections prior to redistricting, four indigenous candidates were elected to this chamber in 2000 and seven were elected in 2003. Following redistricting, 18 were elected in 2006 and 16 were elected in 2009. However, our own analysis did not find that indigenous nominees were more common in newly formed MCDs than in previous MCDs. This accords with qualitative findings; indigenous organization and party representatives reported that nominations of local authorities to municipal office was a much more common inducement offered to indigenous groups than legislative nominations.


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The authors thank Leonardo Arriola, Svitlana Chernykh, Ruth Berins Collier, David Collier, Danny Hidalgo, María Inclán, Robert Powell, Jasjeet Sekhon, Laura Stoker, Leonard Wantchekon, Jason Wittenberg, three anonymous reviewers, and members of the SCID Editorial collective for suggestions and comments. We also thank seminar participants in U.C. Berkeley’s Comparative Politics Colloquium and Statistics of Causal Inference Seminar, and the Empirical Implications of Theoretical Models Summer Institute for helpful comments, as well as Jonathan Fox and Willibald Sonnleitner for sharing data. An earlier version of this paper was presented at the annual meeting of the 2012 Midwest Political Science Association. We acknowledge Mexico’s Instituto Nacional de Estadística y Geografía and Instituto Federal Electoral for providing census and electoral data.

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Correspondence to Brian Palmer-Rubin.

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Meng, A., Palmer-Rubin, B. Gerrymandering Opposition: Minority-Concentrated Districts and Electoral Competition in Mexico. St Comp Int Dev 52, 64–86 (2017).

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  • Redistricting
  • Minority participation
  • Electoral competition
  • Indigenous politics
  • Mexico