Category Archives: Polarization

State Polarization, 1996-2016

Polarization at the state level is highly varied; some states (CO, TX) are polarizing rapidly, others are stable, and still others are even depolarizing (KS). If you put together all these contradictory trends (see the South, the West), the overall picture of polarization is dampened, even at the regional level, much less the national level.

Nevertheless, taking a long view over two decades, we can easily see how much the divide between Democrats and Republicans has grown. In 1996, even after the 1994 Republican tsunami which took out hordes of moderates, there were plenty of Republicans to the left of some Democrats as well as Democrats to the right of some Republicans.


Compare the states to Congress, seen in the plot below, where we also see increased polarization over 20 years. But Congress was already fairly polarized in 1996 with only a handful of overlapping party members. No more of that today.


Polarization in the West, 1996-2017

I previously posted new visualizations of political polarization in Southern American state legislatures in preparation for a conference honoring the work of legendary political scientist Keith T. Poole. Here’s those same plots for Western state legislatures from 1996-2017 (marked in 4 year intervals plus 2017 preliminary data). As always, polarization is measured as the distance between the Republican and Democratic party medians, averaged across the two chambers. Lines are colored according to which party is polarizing faster.

States in the West are the most polarized, and the fastest polarizing, according to our data. Colorado, California, and Arizona dominate the race to the poles, though other states too like Utah are quickly charging up the rankings.  Colorado only in the past few years has overtaken California for the title of the most polarized state legislature in the country. Hawaii is clearly an outlier, with a liberal Democratic party paired with a liberal Republican party (in the House).

In terms of asymmetric polarization, here too, with the exception of Colorado, Democrats and not Republicans have been polarizing in more states.


Here are the positions of Republican party medians in the West. They’ve polarized quickest in Colorado.


The Democratic slopegraph is more dramatic. Dramatic falls are visible in almost every state except Alaska and Idaho.


Polarization in the South, 1996-2017

I’m working on new visualizations of political polarization in American state legislatures in preparation for a conference honoring the work of legendary political scientist Keith T. Poole. Here’s a slopegraph (inspired by Edward Tufte and powered by Thomas Leeper’s awesome R package) of polarization in Southern state legislatures from 1996-2017 (marked in 4 year intervals plus 2017 preliminary data). This was a period of intense transformation in the South, when the almost-fully Democratic-controlled legislatures transformed into Republican-dominated ones in just two decades. Polarization is measured as the distance between the Republican and Democratic party medians, averaged across the two chambers.

In every single state, the parties have been polarizing. And would you just look at Texas? It was the most polarized in 1996, and it’s only increased its lead in 2017.

The line colors represent whether Republicans or Democrats polarized faster in that state. And, in contrast to Congress, Democrats are polarizing faster more frequently than Republicans in the South, including Texas.


Here are the plots for the Republican and Democratic party medians in the South over this time period to give you a sense of how the parties changed. First the Democrats:


Now the Republicans:


Updated Polarization Plot for 2015-2016

We plan to update our publicly accessible data to include the results of the 2014 election.

In the meantime, here is how the states stack up in terms of polarization. One big change has been the vast increase in polarization in Colorado, which nearly matches California’s polarization. Other rapidly polarizing states include Arizona, Texas, and Missouri.


June 2015 Update to Shor-McCarty State Legislatures Data

Today I posted the individual, legislator-level ideology data as well as the aggregate state and chamber-level data for our state legislature ideology data. The data is free for public download and use. Please cite our data and paper if you use this in your academic work, and/or link back to us in other work.

We have extended the data collection through 2014, and we now have 20,783 unique state legislators in our data, as well as 1,816 chamber-years of aggregate data.

As with previous iterations, we have continued to spend a lot of time and effort cleaning up the data; there should be far fewer noise-related issues. But please let us know if you see particular problems.

You can find the individual data here and the state level data here.

Bugs should be reported to us.

The roll call data collection in this update has been supported financially by the Laura and John Arnold Foundation.

State Legislative Ideology and Polarization in 2013-14

Today we posted the July 2014 update to our state legislative aggregate ideology data. One of the major features to this data release has been the incorporation of much more current roll call (1993-2013) and candidate survey (1996-2014) data. All in all, we have added about 25% more chamber-years of data.

Here’s a look at the average legislative ideology  nearly all 50 states that we have data on in 2013-2014 (the data is from 2013 but nearly all states have elections in even-numbered years, hence the data apply to 2014 as well). Higher numbers are more conservative, lower numbers are more liberal. In 2013, Oklahoma had the most conservative state legislature, followed by Arkansas, Tennessee, and Idaho. If Congress were a state, 18 states would be more conservative than it!

New York was the most liberal state legislature in the country, followed by Connecticut, California, Vermont, and Hawaii.


And the equivalent plot for polarization in 2013.

California, once again, leads the country in the ideological divide between the Republican and Democratic parties. Colorado and Arizona are close behind, gaining ground over time.

At the other end, Rhode Island, Arkansas, and Louisiana represent the least polarized legislatures. Note that Nebraska is not in this group. This is despite the fact that the Unicameral is officially nonpartisan in its organization and elections. Nebraska’s hidden parties are polarizing quite quickly.



Asymmetric Polarization in the State Legislatures? Yes and No

Last week I showed how American state legislatures are largely polarizing over the past 15 years or so; the parties are getting ever more extreme and distant from each other, above and beyond the levels of the past. I ended that post with a question: “But which parties are driving this polarization at the state level? Are both parties at fault, or is one becoming more extreme compared to the other? That is, is state legislative polarization symmetric or asymmetric?” I will tackle this subject in my this post.

When we look at Congress over the past 20 years, we can clearly see that–in both the US House and Senate–the Republican party has gotten more extreme over time relative to the Democrats (though in the House Democrats have polarized to a smaller degree as well). This is a familiar story of asymmetric polarization. In fairness, Democrats’ move in the liberal direction started earlier than Republicans: the 1940s versus the mid 1970s. Still, in recent years, Congressional Republicans have unquestionably moved further, faster.


The data and method that Nolan McCarty and I have developed shed light on trends in America’s state legislatures. Let’s look at the picture graphically, plotting party medians over time, separately for each chamber (click on the graphic for a higher-resolution version). By convention, more positive scores represent more conservative preferences, and more negative scores represent liberal preferences.


Looking across the states, Republicans on the whole are clearly polarizing faster than Democrats. In 57 of the 99 state legislative chambers, they are getting more conservative over time, while in 47 chambers Democrats are getting more liberal. In 26 chambers Democrats are actually getting more conservative (eg, depolarizing), while the converse is true in 20 chambers for Republicans where they are getting more liberal. In 26 chambers Democrats are roughly stable and the same is true in 22 chambers for Republicans.

But what the data clearly reveal is that states are wildly diverse. In some states like Tennessee and Colorado, Republicans are getting more extreme in recent time, while Democrats are not changing much. But in other states like Idaho, Mississippi, and California, it is Democrats who are largely responsible for the states’ recent polarization. And finally, there are states like Texas, Missouri, and Nebraska where both parties are polarizing roughly equally and simultaneously.

So the polarization story is similar in some ways in state legislatures than in Congress: Republicans are leading the charge to the ideological poles on average. But it’s different, too: the average story obscures lots of differences across states. State polarization trends thus underline the usefulness of studying state legislatures as a laboratory for political observers: there’s just lots of variation to work with in trying to understand what causes what. And so we should look to state experiences to see whether reforms in areas like redistricting, primaries, campaign finance, and so on do anything to mitigate polarization, and whether some reforms might have unintended consequences that make it worse.