Political Polarization Reaches Historic Highs in U.S. Congress

Introduction

Political polarization of the American electorate is an often discussed topic. The concept is often used to explain political extremism and violence, but also to explain the disintegration of community spirit and mores. Many news sources have touched on the topic in the past like:
Pew’s Political Polarization in the American Public and the Atlantic’s How the American Two-Party System Became so Divided are fairly representative. In an effort to find some more data on the topic, I went to Voteview which maintains a dataset on political polarization. When the original document was written in Markdown, I knew that these folks were serious about data! They honored the tenets of reproducible research by furnishing both the data and the code. The data can be downloaded here. The data were super clean and plotted exactly like the furnished plots. Made several changes to simply the presentation and scale the y-axis from 0 to 1. Additionally, the plots were designed in an aspect ratio of 5” x 9” which is the aspect ratio of the iPhone. The charts should look really nice when viewed on an iPhone.

Three Charts on Congressional Polarization

Table 1 —Top 20 Most Polarized Sessions for the Senate

Rank Year Congress Chamber Mean Diff.
1 2017 115 Senate 0.82
2 2015 114 Senate 0.82
3 1899 56 Senate 0.81
4 1897 55 Senate 0.81
5 1905 59 Senate 0.80
6 2013 113 Senate 0.80
7 1903 58 Senate 0.79
8 1907 60 Senate 0.79
9 1909 61 Senate 0.78
10 1901 57 Senate 0.77
11 1895 54 Senate 0.77
12 1889 51 Senate 0.77
13 1881 47 Senate 0.76
14 1893 53 Senate 0.76
15 1883 48 Senate 0.76
16 1891 52 Senate 0.75
17 1879 46 Senate 0.75
18 1887 50 Senate 0.75
19 1885 49 Senate 0.74
20 2011 112 Senate 0.74

Table 2—Top 20 Most Polarized Sessions for the House

Rank Year Congress Chamber Mean Diff.
1 2017 115 House 0.88
2 2015 114 House 0.88
3 2013 113 House 0.87
4 2011 112 House 0.86
5 1895 54 House 0.84
6 1905 59 House 0.82
7 1897 55 House 0.82
8 1901 57 House 0.82
9 1903 58 House 0.81
10 2005 109 House 0.81
11 2007 110 House 0.81
12 2009 111 House 0.80
13 1899 56 House 0.80
14 1907 60 House 0.80
15 1889 51 House 0.80
16 2003 108 House 0.79
17 1893 53 House 0.79
18 2001 107 House 0.79
19 1879 46 House 0.79
20 1881 47 House 0.78