Political Polarization

Updated 19 January 2014

Recent Papers

"Why Hasn't Democracy Slowed Rising Inequality?" (with Adam Bonica, Nolan McCarty andHoward Rosenthal, August 2013)

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

"Political Fortunes: On Finance and its Regulation" (with Nolan McCarty, Tom Romer, and Howard Rosenthal, Fall 2010). (This paper is theprotoplasm of our forthcoming book:Political Bubbles: Financial Crises and the Failure of American Democracy)

"Does Gerrymandering Cause Polarization?" (with Nolan McCarty andHoward Rosenthal, July 2009)

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

"The Polarization of American Politics" (with Howard Rosenthal, November 1984)

Graphs

Below are graphs of the difference between the Republican and Democratic Partymeans on the firstDW-NOMINATE dimension from the end of Reconstruction throughthe the first session (2013) of the 113^th Congress. This difference in first dimension means is agood measure of . Bythis measure polarization is now at a post-Reconstruction high in the House and Senate.

With few exceptions, roll call voting throughout American history has beensimply structured. Only two dimensions are required to account for the greatbulk of roll call voting. The primary dimension is the basic issue of therole of the government in the economy, in modern terms .The second dimension picked upregional differences within the United States -- first slavery, then bimetalism,and after 1937, Civil Rights for African-Americans. With the passage ofthe 1964 Civil Rights Act, the 1965 VotingRights Act, and the 1968 Open Housing Act, this second dimension slowlydeclined in importance and is now almost totally absent. Race relatedissues - affirmative action, welfare, Medicaid, subsidized housing, etc. -are now questions ofredistribution. and theold split in the Democratic Party between North and South has largelydisappeared. Voting in Congress is now almost purely one-dimensional -a single dimension accounts for about 93 percent of roll call voting choicesin the 113^th House and Senate - and the two parties are increasinglypolarized.

Polarization declined in both chambers from roughly thebeginning of the 20th Century until World War II. It was then fairly stable until the late1970s and has been increasing steadily over the past 25 years. Our(Poole and Rosenthal, 1997)original D-NOMINATEestimation ended with the 99th Congress. Interestingly, Congresses 100-113, if anything, mark an acceleration of the trend (especially in the House). Note,however, that the acceleration is smooth and does not show a particular jump inpolarization induced by the large Republican freshman class elected in 1994.

In addition, the percentage of moderate Representatives and Senators continues to plummet. Inthe House the percentage of moderates (-.25 to +.25 on the firstDW-NOMINATE dimension) has declined to about 10 Percent in bothChambers.

Below are a number of graphs that display the polarization of the parties in Congress since 1879. After the graphs wehave links to the data used to construct them in a variety of formats.

The format of the Polarization Data files is:

 1.  Congress Number 2.  First Year of the Congress 3.  Difference in Party Means - first dimension 4.  Moderates 5.  Percentage of moderate Democrats 6.  Percentage of moderate Republicans 7.  Overlap 8.  Percentage of overlapping Democrats  9.  Percentage of overlapping Republicans10.  Chamber Mean - first dimension11.  Chamber Mean - second dimension12.  Democratic Party Mean - first dimension13.  Democratic Party Mean - second dimension14.  Republican Party Mean - first dimension15.  Republican Party Mean - second dimension16.  Northern Democrat Mean - first dimension17.  Northern Democrat Mean - second dimension18.  Southern Democrat Mean - first dimension19.  Southern Democrat Mean - second dimension