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The Ideological Mapping of American Legislatures

  • BORIS SHOR (a1) and NOLAN McCARTY (a2)

The development and elaboration of the spatial theory of voting has contributed greatly to the study of legislative decision making and elections. Statistical models that estimate the spatial locations of individual decision-makers have made a key contribution to this success. Spatial models have been estimated for the U.S. Congress, the Supreme Court, U.S. presidents, a large number of non-U.S. legislatures, and supranational organizations. Yet one potentially fruitful laboratory for testing spatial theories, the individual U.S. states, has remained relatively unexploited, for two reasons. First, state legislative roll call data have not yet been systematically collected for all states over time. Second, because ideal point models are based on latent scales, comparisons of ideal points across states or even between chambers within a state are difficult. This article reports substantial progress on both fronts. First, we have obtained the roll call voting data for all state legislatures from the mid-1990s onward. Second, we exploit a recurring survey of state legislative candidates to allow comparisons across time, chambers, and states as well as with the U.S. Congress. The resulting mapping of America's state legislatures has great potential to address numerous questions not only about state politics and policymaking, but also about legislative politics in general.

Corresponding author
Boris Shor is Assistant Professor, Harris School of Public Policy Studies, University of Chicago, 111E. 60th Street, Suite 185, Chicago, IL 60637 (
Nolan McCarty is Susan Dod Brown Professor of Politics and Public Affairs, Woodrow Wilson School, Princeton University, 424 Robertson Hall, Princeton, NJ 08544 (
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This list contains references from the content that can be linked to their source. For a full set of references and notes please see the PDF or HTML where available.

Charles M. Cameron 2000. Veto Bargaining: Presidents and the Politics of Negative Power. New York: Cambridge University Press.

Simon Hix , Abdul Noury , and Gerard Roland . 2007. Democratic Politics in the European Parliament. New York: Cambridge University Press.

John B. Londregan 2000b. Legislative Institutions and Ideology in Chile. New York: Cambridge University Press.

Seth Masket . 2009. No Middle Ground: How Informal Party Organizations Control Nominations and Polarize Legislatures. Ann Arbor: University of Michigan Press.

Keith T. Poole 2005. Spatial Models of Parliamentary Voting. Cambridge: Cambridge University Press.

Sean M. Theriault 2008. Party Polarization in Congress. Cambridge: Cambridge University Press.

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American Political Science Review
  • ISSN: 0003-0554
  • EISSN: 1537-5943
  • URL: /core/journals/american-political-science-review
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Supplementary Materials

Shor and McCarty supplementary material

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