Unintentional Gerrymandering: Political Geography and Electoral Bias in Legislatures

While conventional wisdom holds that partisan bias in U.S. legislative elections results from intentional partisan and racial gerrymandering, we demonstrate that substantial bias can also emerge from patterns of human geography. We show that in many states, Democrats are inefficiently concentrated in large cities and smaller industrial agglomerations such that they can expect to win fewer than 50% of the seats when they win 50% of the votes. To measure this ‘‘unintentional ∗ The authors wish to thank Micah Altman, Pablo Beramendi, Kyle Dropp, David Epstein, Andrew Gelman, Tony Hill, Nolan McCarty, Michael McDonald, Boris Shor, John Sides, and Chris Warshaw for helpful comments and suggestions. Online Appendix available from: http://dx.doi.org/10.1561/100.00012033 app Supplementary Material available from: http://dx.doi.org/10.1561/100.00012033 supp MS submitted 4 April 2012 ; final version received 13 January 2013 ISSN 1554-0626; DOI 10.1561/100.00012033 c © 2013 J. Chen and J. Rodden