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. Access through your institution Buy or subscribe This is a preview of subscription content,

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about institutional subscriptions * Read our FAQs * Contact customer support SIMILAR CONTENT BEING VIEWED BY OTHERS EXPLAINING CHANGES IN US RESIDENTIAL SEGREGATION THROUGH PATTERNS OF

POPULATION CHANGE Article 09 February 2024 HUMAN MOBILITY PATTERNS ARE ASSOCIATED WITH EXPERIENCED PARTISAN SEGREGATION IN US METROPOLITAN AREAS Article Open access 16 June 2023 A DATASET OF

US PRECINCT VOTES ALLOCATED TO CENSUS GEOGRAPHIES WITH PRECISION Article Open access 15 May 2025 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. CHANGE

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America’s Great Divide_ (Houghton Mifflin, 2018). Download references 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. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS *

Institute for Quantitative Social Science, Harvard University, Cambridge, MA, USA Jacob R. Brown & Ryan D. Enos * Department of Government, Harvard University, Cambridge, MA, USA Jacob

R. Brown & Ryan D. Enos Authors * Jacob R. Brown View author publications You can also search for this author inPubMed Google Scholar * Ryan D. Enos View author publications You can also

search for this author inPubMed Google Scholar 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. ETHICS DECLARATIONS COMPETING INTERESTS 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. SUPPLEMENTARY INFORMATION SUPPLEMENTARY INFORMATION

Supplementary Methods, Supplementary Results, Supplementary Figs. 1–27, Supplementary Tables 1–20 and Supplementary References. REPORTING SUMMARY PEER REVIEW INFORMATION RIGHTS AND

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ARTICLE CITE THIS ARTICLE Brown, J.R., Enos, R.D. The measurement of partisan sorting for 180 million voters. _Nat Hum Behav_ 5, 998–1008 (2021). https://doi.org/10.1038/s41562-021-01066-z

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