The Polarization of the Congressional Parties

Updated 12 June 2018

Recent Papers

Polarized America: The Dance of Ideology and Unequal Riches (2nd edition). Cambridge, MA: MIT Press, 2016 (With Nolan M. McCarty and Howard Rosenthal).

Adam Bonica, Nolan McCarty, Keith T. Poole, and Howard Rosenthal. 2015. "Congressional Polarization and its Connection to Income Inequality." American Gridlock: The Sources, Character, and Impact of Congressional Polarization, Chapter 16, pp. 357-377, edited by James A. Thurber and Antoine Yoshinaka. New York: Cambridge University Press, 2015.

Christopher Hare and Keith T. Poole. 2014. "The Polarization of Contemporary American Politics." Polity, 46:411-429.

Adam Bonica, Nolan McCarty, Keith T. Poole, and Howard Rosenthal. 2013. "Why Hasn't Democracy Slowed Rising Inequality?" Journal of Economic Perspectives, 27(3): 103-24.

"Picture of a Polarized Congress" (UGAresearch, the research magazine of the University of Georgia, 2012) (PDF: Picture of a Polarized Congress)

Nolan McCarty, Keith T. Poole, Thomas Romer, and Howard Rosenthal. 2010. "Political Fortunes: On Finance and its Regulation." Daedalus, 139-4:1-13. (This paper is the protoplasm of our 2013 book: Political Bubbles: Financial Crises and the Failure of American Democracy)

Nolan McCarty, Keith T. Poole, and Howard Rosenthal. 2009. "Does Gerrymandering Cause Polarization?" American Journal of Political Science, 53 (July):666-680.

"Growing Apart: The Mathematical Evidence for Congress' Growing Polarization" (by Jordan Ellenberg, Slate Magazine, 26 December 2001)

Keith T. Poole and Howard Rosenthal. 1984. "The Polarization of American Politics." Journal of Politics, Vol. 46, No. 4 (November).


Below are graphs of the difference between the Republican and Democratic Party means on the first DW-NOMINATE dimension from the end of Reconstruction through the the first session (2017) of the 115th Congress. This difference in first dimension means is a good measure of the level of political polarization. By this measure polarization is now at a post-Reconstruction high in the House and Senate.

To see the graphs go to the new Voteview website at UCLA:

New Polarization Graphs

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