Partisan motivations for redistricting have existed since the first US Congress. George Washington, a Federalist, claimed that Virginia districts were “arranged as to place a large proportion of those who are called Antifederalists in that Station” (Hunter Reference Hunter2011). Similar motivations remain but redistricting now determines the balance of power between Democrats and Republicans. Former Speaker of the House, Newt Gingrich (R-GA), claimed that Democrats “get to rip off the public in the states where they control and protect their incumbents, and we get to rip off the public in the states where we control and protect our incumbents” (Eilperin Reference Eilperin2006).
To remedy the conflict of interest apparent in legislative redistricting, reformers have proposed to create independent commissions responsible for redistricting. However, the efficacy of redistricting reforms is contested in political science. Some studies indicate that districts drawn by non-legislative institutions are more competitive than districts drawn by state legislatures (Carson, Crespin, and Williamson Reference Carson, Crespin and Williamson2014; Lindgren and Southwell Reference Lindgren and Southwell2013; McDonald Reference McDonald2006). Other studies find that redistricting institutions have little effect on electoral competition (Abramowitz, Alexander, and Gunning Reference Abramowitz, Alexander and Gunning2006; Forgette, Garner, and Winkle Reference Forgette, Garner and Winkle2009; Henderson, Hamel, and Goldzimer Reference Henderson, Hamel and Goldzimer2018; Masket, Winburn, and Wright Reference Masket, Winburn and Wright2012).
This research extends the work of Carson, Crespin, and Williamson (Reference Carson, Crespin and Williamson2014) by separating independent and political commissions, which were grouped together despite different institutional designs. I analyzed US House of Representatives elections from 1982 to 2018 and found that—relative to legislative redistricting—independent commissions are 2.25 times more likely to have competitive elections, and they decrease incumbent party wins by 52%.
Previous research on independent redistricting commissions may have found null results because of small sample sizes and a lack of statistical power. Table 1 shows the data used in existing redistricting research, and figure 1 shows the percentage of districts drawn by independent commissions in the past four redistricting cycles. My research adds new data from the 2010 redistricting cycle, in which 17% of US House districts were drawn by independent commissions.
Data Used in Redistricting Research
Percentage of Independent-Commission–Drawn Districts
INSTITUTIONAL DESIGN AND ELECTORAL COMPETITION
The US Constitution mandates that each state redraw its congressional districts after the decennial census, but it does not delegate responsibility to a specific institution. State legislatures draw most congressional districts with district maps created in legislative committees, and they are subject to a vote in both chambers before requiring the governor’s signature. Other states use a political commission to draw their district lines. The design of political commissions varies, with some states allowing the political commission to directly enact district maps and other states requiring legislative approval. Independent commissions separate the legislature from the redistricting process even further by prohibiting legislators from being members. Finally, in some instances, and due to legislative inaction or litigation, the courts are required to draw district boundaries (Levitt Reference Levitt2019). Figure 2 shows the number of districts for which different redistricting institutions were responsible in the 2018 election. In 2018, there were 428 drawn congressional districts and seven states with one at-large congressional district.
2018 Redistricting Institutions
Mapmakers can affect electoral competition by packing minority-party voters into safe districts to waste their votes or by spreading out minority- party voters to splinter their support (Carson and Crespin Reference Carson and Crespin2004). All states are mandated to draw districts as equal in population as possible and are prohibited from discriminating based on race; however, states are allowed to establish their own additional criteria. Typical redistricting criteria include compactness, contiguity, preservation of communities of interest, and preservation of prior districts. Some states have criteria related to incumbent protection, such as avoiding districts that would create an election between incumbents and prohibiting (or explicitly allowing) mapmakers to favor incumbents. I expected the institutional design of redistricting institutions to affect electoral competition because of the different motivations of members and the constraints placed by rules.
Legislators are motivated by their own reelection and the success of their party (Aldrich Reference Aldrich1995; Cox and McCubbins Reference Cox and McCubbins2005; Mayhew Reference Mayhew1974). Redistricting can be used to achieve these goals by creating safe districts where members of the incumbent party are heavily favored to win the election. When redistricting is controlled by the state legislature, district maps are treated like normal legislation and biased district maps can be enacted by a self-interested partisan majority. I expected state legislative redistricting to be associated with less-competitive elections than other types of redistricting institutions.
When redistricting is controlled by the state legislature, district maps are treated like normal legislation and biased district maps can be enacted by a self-interested partisan majority.
The members of political commissions are either legislators or are chosen by legislators; therefore, self-interested motivations are likely. However, unlike legislative redistricting, political commissions are designed to give voice to the minority party. For example, Hawaii’s congressional lines are drawn by a nine-member commission in which the majority and minority party leaders in each chamber choose two members and then those eight members choose the ninth member (Levitt Reference Levitt2019). In addition to membership rules that countervail partisan motivations, political commissions are constrained by redistricting criteria. In Hawaii, the redistricting commission is not allowed to draw districts that “unduly favor a person or political faction” (Carson and Crespin Reference Carson and Crespin2004). I expected political commissions to be associated with more competitive elections than state legislatures.
Independent redistricting commissions are designed to function like juries, and legislators and party operatives are prohibited from being members. For example, to be eligible to be a commissioner in California, you and your family members could not have been a candidate, lobbyist, legislative staff, party employee, or large donor within the past 10 years. Furthermore, California’s independent commission has five Democrats, five Republicans, and four Independents to promote impartiality (Levitt Reference Levitt2019). Independent redistricting commissioners may have some partisan motivations; however, unlike members of political commissions and state legislatures, there are formal rules against running for office in the districts created. Furthermore, the independent redistricting states all have additional criteria aimed toward creating competitive elections. For example, Arizona’s constitution states: “[T]o the extent practicable, competitive districts should be favored where to do so would create no significant detriment to the other goals.” Likewise, commissioners are prohibited from using partisan data when drawing district lines in California (National Conference of State Legislatures 2019a, 2019b). I expected independent commissions to be associated with more competitive elections than other types of redistricting institutions.
Independent redistricting commissions are designed to function like juries, and legislators and party operatives are prohibited from being members.
Court-administered redistricting gives judges the authority to make new district maps. Judges are expected to apply legal principles neutrally. However, existing research shows that mapmaking judges have a “mask of neutrality” in which they draw districts that increase competitiveness while advancing their preferred party’s interests (Grose Reference Grose2011; Peterson Reference Peterson2019). Peterson (Reference Peterson2019) found that Democratic judges increase electoral competition by adding Democratic voters to Republican-held districts. I expected court redistricting to be associated with more competitive elections than state legislative redistricting.
EMPIRICAL STRATEGY
I analyzed redistricting institutions and electoral competition through three district-level variables: incumbent party wins; semi-competitive elections (i.e., the Democrat’s share of the two-party vote between 40% and 60%); and competitive elections (i.e., the Democrat’s share of the two-party vote between 45% and 55%). Election data were retrieved from Jacobson (Reference Jacobson2020) and include all US House elections from 1982 to 2018 for states that conducted redistricting (i.e., those that have multiple districts). Redistricting data were retrieved from Peterson (Reference Peterson2019), Levitt (Reference Levitt2019), and Ballotpedia (2020). I hypothesized that independent commissions would be associated with fewer incumbent wins and more semi-competitive and competitive elections than legislative redistricting. Similarly, I hypothesized that political commissions and courts would be associated with fewer incumbent wins and more semi-competitive and competitive elections than legislative redistricting, but to a lesser degree than independent commissions.
To test my hypotheses, I estimated logistic regression models. The independent variables of interest were indicator variables for the different redistricting institutions with legislative-drawn districts as the reference category. Independent Commission was 1 if a district was drawn by an independent redistricting commission and 0 otherwise. Political Commission was 1 if a district was drawn by a political redistricting commission and 0 otherwise. Court was 1 if a district was drawn by a court and 0 otherwise. The dependent variables were different binary measures of electoral competition. Incumbent Party Win was 1 if the incumbent party won the district and 0 otherwise. Semi-Competitive was 1 if a district was semi-competitive and 0 otherwise. Competitive was 1 if a district was competitive and 0 otherwise.
Fixed effects, clustered standard errors, and control variables were included in the regression models to improve statistical precision (table 2). State and year fixed effects isolated the relationship between redistricting institutions and electoral competition by controlling for state-to-state and year-to-year differences that were unobserved in the data. Clustered standard errors accounted for the correlation between observations within each state. I used the same control variables as Carson, Crespin, and Williamson (Reference Carson, Crespin and Williamson2014). The control variables were known correlates of election competition but were exogenous to the redistricting process (Nelson Reference Nelson2022). South was 1 if the state was one of the 13 Southern states recognized by the Confederacy and 0 otherwise. Open Seat was 1 if the district held an open-seat election and 0 otherwise. Quality Challenger was 1 if the challenger previously held elective office and 0 otherwise. Spending was the natural logarithm of the combined expenditures of the Republican and Democratic candidates. Partisanship was the absolute value of the two-party Democratic presidential vote percentage for the entire nation minus the two-party Democratic presidential vote percentage in each district.
Logistic Regression
Notes: ***p<0.001; **p<0.01; *p<0.05.
For the purpose of interpretation, the logit coefficients from the model were exponentiated to create odds ratios. Odds ratios can be interpreted as the odds that an outcome occurs given a particular treatment compared to the odds of the outcome occurring without that treatment (table 3). Figure 3 graphically presents the odds-ratio results for competitive elections.
Odds-Ratio Conversion, Relative to Legislative Redistricting
Notes: ***p<0.001; **p<0.01; *p<0.05.
Odds Ratio for Competitive Elections with Confidence Intervals
RESULTS
Compared to states with legislative redistricting, states with independent redistricting commissions had fewer incumbent-party wins, more semi-competitive elections, and more competitive elections. The odds-ratio conversion indicates that independent commission districts were 0.48 times less likely to have the incumbent party win, 3.01 times more likely to have a semi-competitive election, and 2.25 times more likely to have a competitive election (see table 3). These results are statistically significant and robust to various modeling specifications.Footnote 1
Compared to states with legislative redistricting, states with independent redistricting commissions had fewer incumbent-party wins, more semi-competitive elections, and more competitive elections.
Political-commission–drawn districts have fewer incumbent party wins and more competitive elections than districts drawn by state legislatures, but they are less likely to produce semi-competitive elections. However, the differences between political-commission–drawn districts and state legislative districts were not statistically significant (see table 3).
Court-drawn districts were 1.51 times more likely to have competitive elections than districts drawn by state legislatures, but there was no statistical difference between court and legislative redistricting in incumbent-party success or semi-competitive elections (see table 3). This result supports existing research that argues that courts increase competitiveness while advancing their preferred party’s interests (Peterson Reference Peterson2019).
CONCLUSION
Electoral competition is essential to democratic accountability; however, since the 2010 redistricting cycle, the incumbent party has won 94% of congressional elections. I argue that the lack of competitiveness is driven by the design of redistricting institutions. Redistricting conducted by legislators will be influenced by self-interest due to their reelection motivations, whereas independent commissions remove legislators from the process and place formal constraints on mapmakers. I found a strong, statistically significant relationship between independent redistricting commissions and more competitive elections and fewer incumbent party wins. California—which completely removes the state legislature from redistricting by using an external body to select commissioners—exemplifies the potential effects of institutional reform. In the decade before independent commissions were implemented, only 5.2% of districts in California had a competitive election; since removing redistricting authority from the state legislature, the percentage of competitive districts has increased to 14.6%.
DATA AVAILABILITY STATEMENT
Research documentation and data that support the findings of this study are openly available at the PS: Political Science & Politics Harvard Dataverse at https://doi.org/10.7910/DVN/N8WNB1.
Supplementary Materials
To view supplementary material for this article, please visit https://doi.org/10.7910/DVN/N8WNB1.
CONFLICTS OF INTEREST
The author declares that there are no ethical issues or conflicts of interest in this research.
FUNDING
The author did not receive any financial support for this research.
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