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The measurement of partisan sorting for 180 million voters

Abstract

Segregation across social groups is an enduring feature of nearly all human societies and is associated with numerous social maladies. In many countries, reports of growing geographic political polarization raise concerns about the stability of democratic governance. Here, using advances in spatial data computation, we measure individual partisan segregation by calculating the local residential segregation of every registered voter in the United States, creating a spatially weighted measure for more than 180 million individuals. With these data, we present evidence of extensive partisan segregation in the country. A large proportion of voters live with virtually no exposure to voters from the other party in their residential environment. Such high levels of partisan isolation can be found across a range of places and densities and are distinct from racial and ethnic segregation. Moreover, Democrats and Republicans living in the same city, or even the same neighbourhood, are segregated by party.

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Fig. 1: Spatial and aspatial measures of segregation.
Fig. 2: Measuring spatial exposure across increasingly small geographies.
Fig. 3: Nationwide distribution of partisan spatial isolation and exposure.
Fig. 4: Isolation by density and urban area.
Fig. 5: Relative exposure by geography.
Fig. 6: Nationwide percentiles of partisan exposure by party and race.

Data availability

Anonymized replication data are available in the Harvard University Dataverse at https://doi.org/10.7910/DVN/A40X5L.

Code availability

All replication code are available in the Harvard University Dataverse at https://doi.org/10.7910/DVN/A40X5L.

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Acknowledgements

The authors received no specific funding for this work. We thank B. Lewis and D. Kakkar at the Harvard Center for Geographic Analysis, the Harvard MIT Data Center, and A. Dagonel for research assistance; M. Schwenzfeier and J. Rodden for advice on research design; A. Agadjanian for help making sense of the precinct data; N. Cohn for providing survey data on the age distribution of voters in Wisconsin; and seminar participants at the University of Pittsburgh, New York University, Northeastern University, Princeton University, Brown University, University of Massachusetts at Amherst and Harvard University.

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Authors

Contributions

J.R.B. and R.D.E. both contributed to the conception, design, analysis, data collection, and writing.

Corresponding authors

Correspondence to Jacob R. Brown or Ryan D. Enos.

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The authors declare no competing interests.

Additional information

Peer review information Nature Human Behaviour thanks M. Keith Chen and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Aisha Bradshaw.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Spatial versus Aspatial Exposure/Isolation.

Nationwide distribution (n = 180,660,202) of individual spatial (left) and aspatial (right) partisan isolation and exposure separately for Democrats (blue) and Republicans (red). Solid vertical lines represent mean values and dashed lines represent median values. The distributions are weighted by the posterior partisan probabilities.

Extended Data Fig. 2 Individual Differences in Spatial versus Aspatial Exposure/Isolation.

Nationwide distribution (n = 180,660,202) of individual-level changes in partisan Exposure and Isolation separately for Democrats (blue) and Republicans (red). The histograms on the left show the percentage point difference in spatial and aspatial exposure, while the histograms on the right show the percent change. Solid vertical lines represent mean values and dashed lines represent median values. The distributions are weighted by the posterior partisan probabilities.

Extended Data Fig. 3 Individual Absolute Differences in Spatial versus Aspatial Exposure/Isolation.

Nationwide distribution (n = 180,660,202) of individual-level absolute changes in partisan Exposure and Isolation separately for Democrats (blue) and Republicans (red). The histograms on the left show the percentage point absolute difference in spatial and aspatial exposure, while the histograms on the right show the absolute percent change. Solid vertical lines represent mean values and dashed lines represent median values. The distributions are weighted by the posterior partisan probabilities.

Extended Data Fig. 4 Exposure and Isolation with Imputation Versus Without Imputation.

Nationwide distribution (n = 180,660,202) of individual spatial partisan isolation and exposure with imputation of partisanship (left) and without (right) separately for Democrats (blue) and Republicans (red). Solid vertical lines represent mean values and dashed lines represent median values. The distribution on the left is weighted by the posterior partisan probabilities.

Extended Data Fig. 5 Percent self-report Partisan Category by Posterior Partisan Probability.

LOESS lines plotting the relationship between posterior partisan probability (Republicans on top, Democrats on bottom) and the rates of survey respondents reporting as the corresponding partisanship. The correlation is limited to the subset of survey respondents (n = 7, 087) who are not registered with a major political party. Black lines plot the LOESS curve with survey weights incorporated, red/blue lines without survey weights. The 45-degree grey line plots a perfect 1-to-1 relationship between posterior partisan probability and self-reported partisanship. The horizontal dotted lines show the rates at which survey respondents who are registered Democrats/Republicans self-report partisanship in agreement (or disagreement for the lower lines) with their actual partisan registration. That is, the upper blue (red) dotted line represents the proportion of survey respondents we know are registered Democrats (Republicans) who self-report as Democrats (Republicans), and the lower dotted line represents the proportion who do not self-report as Democrats (Republicans). These lines represent lower and upper bounds on how accurate we can expect our forecast to appear when measured against survey data. The histogram on the bottom plots the frequency distribution of posterior partisan probabilities across the unaffiliated subset.

Extended Data Fig. 6 Partisan Segregation vs. non-Hispanic White-only Partisan Segregation.

Distribution for non-Hispanic white voters (n = 115,736,045) of differences between partisan segregation calculated from all 1,000 nearest neighbors and partisan segregation calculated only from non-Hispanic white neighbors. Positive Isolation values means that a voter appears less isolated by partisanship when we look only at their non-Hispanic white neighbors. Positive Exposure values means that a voter appears to have less cross-party exposure when we only look at their white neighbors. Distributions are plotted separately for Democrats (blue) and Republicans (red). Solid lines represent mean values and dashed lines represent median values. Distributions are weighted by posterior partisan probabilities.

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Supplementary Methods, Supplementary Results, Supplementary Figs. 1–27, Supplementary Tables 1–20 and Supplementary References.

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Brown, J.R., Enos, R.D. The measurement of partisan sorting for 180 million voters. Nat Hum Behav (2021). https://doi.org/10.1038/s41562-021-01066-z

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