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Geography, Uncertainty, and Polarization

  • Nolan McCarty, Jonathan Rodden, Boris Shor, Chris Tausanovitch and Christopher Warshaw...

Using new data on roll-call voting of US state legislators and public opinion in their districts, we explain how ideological polarization of voters within districts can lead to legislative polarization. In so-called “moderate” districts that switch hands between parties, legislative behavior is shaped by the fact that voters are often quite heterogeneous: the ideological distance between Democrats and Republicans within these districts is often greater than the distance between liberal cities and conservative rural areas. We root this intuition in a formal model that associates intradistrict ideological heterogeneity with uncertainty about the ideological location of the median voter. We then demonstrate that among districts with similar median voter ideologies, the difference in legislative behavior between Democratic and Republican state legislators is greater in more ideologically heterogeneous districts. Our findings suggest that accounting for the subtleties of political geography can help explain the coexistence of polarized legislators and a mass public that appears to contain many moderates.

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Nolan McCarty is the Professor in the Department of Politics, the Woodrow Wilson School, Princeton University, 212 Robertson Hall, Princeton, NJ 08544 ( Jonathan Rodden is the Professor in the Department of Political Science and Senior Fellow in the Hoover Institution, Stanford University, Encina Hall Central, Room 444, Stanford, CA 94305 ( Boris Shor is an Assistant Professor in the Department of Political Science, University of Houston, 389 Phillip Guthrie Hoffman Hall, Houston, TX 77004 ( Chris Tausanovitch is an Assistant Professor in the Department of Political Science, 3383 Bunche Hall, UCLA, Los Angeles, CA 90095 ( Christopher Warshaw is an Assistant Professor in the Department of Political Science, George Washington University, 422 Monroe Hall, 2115 G St. NW, Washington, DC 20052 ( Earlier versions of this paper were presented at the 2013 Annual Meetings of the American Political Science Association, the 2014 Conference on the Causes and Consequences of Policy Uncertainty at Princeton University, the 2014 European Political Science Association, and the Princeton Geneva Conference on Political Representation. The authors thank seminar participants at the Institute for Advanced Study, Harvard, Northwestern, and the DC area political science group. The authors thank Project Votesmart for access to NPAT survey data. The roll-call data collection has been supported financially by the John and Laura Arnold Foundation, Russell Sage Foundation, the Princeton University Woodrow Wilson School, the Robert Wood Johnson Scholar in Health Policy program, and NSF Grants SES-1059716 and SES-1060092. Special thanks are due to Michelle Anderson and Peter Koppstein for running the roll-call data collection effort. The authors also thank the following for exemplary research assistance: Steve Rogers, Michael Barber, and Chad Levinson. To view supplementary material for this article, please visit

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Political Science Research and Methods
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