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.



July 2014 Aggregate Data Release

We are releasing a major new version of our state and chamber-level aggregate data. Here are the highlights of the July 2014 release:

  1. In all, we have 342 additional chamber-years of new data, or about 25% more than the previous release.
  2. The data now extend through 2013 for most, but not all, states. Major holes of missing state-years have been filled.
  3. The individual level data underlying this release has been extensively cleaned and remerged to minimize noise inherent in projects like this.

You can find the data here.

The individual level data will be posted very soon, as well.

If you find the data useful, please cite it as well the 2011 article on which the data is based. Feel free to contact us if you have questions about this data.

New Preliminary 2013 Data on Polarization

I (Boris) have a new post over at the Monkey Cage blog at the Washington Post. It summarizes some of the posts I’ve made here, for an audience that probably hasn’t seen this blog before.

The one update is that the posts here used the most recent publicly available version of our aggregate state legislative data. That data includes the years up through 2011. The Monkey Cage post uses a preliminary update to our data set, that brings the data to 2013.

We are working on polishing this data for public release shortly.

In the meantime, here are the new plots using that data set. The graph below shows legislative polarization in each state, averaging across all the years of our data (approximately 1996-2013) and across both legislative chambers. Polarization is defined as the average ideological distance between the median Democrat and Republican in the state legislature.  Larger numbers indicate more division. The dashed line is the level of congressional polarization, included as a comparison (“US”).


About half of the states are even more polarized than Congress—which is saying a lot. At the same time, some states–like Louisiana, Delaware, and Rhode Island–have  relatively less polarized state legislatures. In Louisiana, both parties are fairly conservative, and in Delaware and Rhode Island, they are both fairly liberal.

One state that stands out is California. It is incredibly polarized. (And its most recent primary and redistricting reforms look unlikely to reduce polarization.) Unlike Congress, however, Democrats both dominate the state so thoroughly and no longer need to attain supermajorities to pass budgets, so this polarization is not as much of an obstacle to actual lawmaking in the California state legislature.

Another state that stands out is Wisconsin–the site of massive protests in 2011, a recall campaign against sitting governor Scott Walker, and even a physical fight between Republican and Democratic justices on its state Supreme Court.  It is perhaps no surprise that Wisconsin too is highly polarized.

Not only are states polarized, that polarization has increased over time. The graph below breaks down the trends in the ideology of Democrats and Republicans (measured by party medians) over time and across all 50 states. By convention, more positive scores represent more conservative preferences, and more negative scores represent liberal preferences. (One side-note: a data error exists in Washington State around the year 2000 and is being fixed.)


Most states have polarized over the past 20 years or so, but some more than others. Arizona, California, and Colorado are polarizing very fast. Nebraska—a state without formal political parties in its legislature—is polarizing very quickly too, though from a relatively low base.

Moreover, we are seeing asymmetric polarization, just as in Congress. Republicans have been getting more extreme faster than Democrats in more state legislative chambers, but this is by no means universally true across all states.

All in all, the picture we see in state legislatures is similar in many respects to Congress, but different in key points. The parties are pretty far apart on average, but that difference varies across the states. The parties are increasingly polarizing over time, but that too varies across state. Finally, we see cases of symmetric and asymmetric polarization. These new data on polarization at the state level—and the uneven pace of polarization across states—should help pundits and scholars figure out what’s driving polarization in our statehouses.

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.


Polarization Trends in American State Legislatures by Chamber

The political parties in Congress are increasingly polarized in ideological terms. This is largely driven by replacement rather than adaptation; that is, moderates are increasingly leaving Congress, and being replaced by ideological extremists.

The plot below shows the difference between the Republican and Democratic party medians using Poole et al’s common space NOMINATE scores, for the 103rd (1992-1993) through the 112th (2011-2012) Congresses. Under this common measure, a larger gap between the centers of both parties indicates a greater level of polarization.polarization_congress_years_cs

Both House and Senate are polarized (the distance is greater than zero), and they are getting more so over time. The US House in particular is both more polarized in terms of level and polarizing faster in terms of trend relative to the US Senate.

What about American state legislatures? It’s important to nail down these numbers because we need to know where we stand to find out if polarization is leading to political gridlock and dysfunctional policy. We also need a barometer of polarization to find out whether reforms like opening up primaries, taking redistricting away from politicians themselves, term limits, and so forth can do anything about this yawning gap between the parties. And since there are 50 state legislatures, we might find answers to these questions more quickly and definitively than we can with Congress, of which we only have one.

Earlier in this blog I showed evidence that most state legislatures are in fact quite polarized, and a significant number of them are even more polarized than Congress. The data underlying these figures can be found here, and the paper explaining how Nolan McCarty and I came up with the numbers can be found hereNow we’ll take a more detailed look at the state polarization trends for all 50 states over time. The plot below shows the distances between the party medians for all 50 states over approximately the same time period, roughly 1996-2010.


As with the US Congress, all 99 state legislative chambers (Nebraska has a single chamber commonly referred to as the Unicam, which I term a Senate here) are polarized. In 59 of those 99 chambers, the parties are getting more distant from each other. In 16 of them, the parties are actually depolarizing or getting closer. Finally, in 24 chambers, the parties are roughly stable in relation to each other.

However, in most states, unlike in the US Congress, the upper (Senate) chamber is typically more polarized than the lower (House or Assembly) chamber. On the other hand, the lower chamber is polarizing faster in more states than the upper chamber. It is not yet clear why these differences should exist.

The top 10 fastest polarizing chambers, in order, are the Idaho Senate and House, the Missouri Senate, the Arizona Senate, the Hawaii Senate, the Colorado Senate, the Tennessee House, the Nevada Senate, the Maryland Senate, and Mississippi Senate.

At the same time, California retains its title as the most polarized state legislature in the country. It has even managed to move up a couple of notches in the past 15 years. 

Another notable state is Nebraska, whose Unicam is amongst the fastest polarizers in the country, despite the fact that it is nonpartisan by law in the chambers and at the voting booth. Seth Masket and I show in a paper how parties in the state have overcome this powerful prohibition to work as cohesive, disciplined units–just like other states.

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 next post.

Interestingly enough, a few state chambers are actually depolarizing: the parties are actually coming closer together. The fastest depolarizing state chambers, in order, are the Wyoming House, the Oregon Senate, the Alaska Senate, the Ohio Senate, and the North Carolina Senate. This is completely unheard of in recent years in Congress.

NB: The scales of the two plots aren’t comparable because they are taken from two separate data sources. However, in technical terms, they are both common space measures which disallow individual legislator ideological drift in order to facilitate an apples-to-apples comparison.

Sizing Up Christie’s Appointment Choices in New Jersey: State Legislature

Five-term Sen. Frank Lautenberg (D-NJ) passed away today. Under my former home state New Jersey law, the special election to fill the empty seat will happen in November 2013, which is the regularly scheduled general election for governor and the state legislature. Until then, Governor Chris Christie (R) gets to appoint a replacement.

Naturally, given the tight division of seats between the parties in Congress, and many important battles left to fight until November, speculation has already begun about Christie’s choice. Some names that have been mentioned include three sitting state legislators: Tom Kean, Joe Kyrillos, and Jon Bramnick.

Yet that speculation misses a key variable: the likely voting behavior of Christie’s choice upon entering the Senate. My research with Nolan McCarty can help inform the discussion because it directly measures the ideology of the most likely candidates for the position.

In this post, I’ll discuss the three state legislative candidates that have been mentioned as likely replacements for Lautenberg, and their ideological position, relative to New Jersey Republicans from 1996 to 2008 and the US Congress from the 109th through the 112th Congresses. I will use both legislative voting behavior and candidate responses of all state legislators and members of Congress to generate a single number for each candidate on a left-right ideology scale.

The current state legislative candidates are as follows:

  • State Senator Thomas “Tom” Kean, Jr. His score is 0.041, which is slightly on the right of the state party (65th percentile). 
  • State Senator Joseph “Joe” M. Kyrillos. His score is 0.014, which is a tick to the right of the median of the state party (55th percentile).
  • State Assembly Republican Leader Jon Bramnick. His score is -0.028, which is actually somewhat to the left (40th percentile) of the state party.

Thus, all three are moderate Republicans — in New Jersey, whose party is relatively liberal, compared with state legislators across the country (do note that there is a small amount of error underlying the estimates, so I wouldn’t make too much–for example–about the distinction between Kean and Kyrillos). Here is a graphical representation of where New Jersey Republicans lie in comparative terms (outlined in green near the bottom of the chart). The states are ordered from overall most conservative at the top (Idaho) to most liberal at the bottom (California). The red boxes represent Republicans, and the blue ones Democrats. Medians, or centers of the parties looking across time, are denoted by black marks within the boxes.


But what about in comparison to the US Senate? How conservative or moderate are the three likely to be when they arrive there shortly? My research allows me to simultaneously measure the ideology of sitting and former members of Congress along with more than 18,000 sitting and former state legislators. Thus, I project that Kean, Kyrillos, and Bramnick are approximately comparable to moderate Maine Republican Senators Olympia Snowe and Susan Collins, and former Massachusetts Republican Senator Scott Brown.

The data underlying this post is free and open to the scholarly community and the public. The technical article that explains the approach we used for generating these scores is here.

In another post I’ll discuss New Jersey Republicans who’ve served as members of Congress.

ps The key assumption for this measurement project is that legislators are, on average, consistent in their voting behavior and survey responses, no matter which position they hold. Basically, and roughly speaking, legislators typically don’t change their positions on the whole throughout their political careers. This was the basis of my then-controversial post about Scott Brown’s moderation based on his roll call votes in the Massachusetts State Senate. Luckily, I turned out to be right on that one. More generally, there is much political science evidence on this score.

State Legislatures and Polarization

America’s state legislatures are polarized–just like Congress–between liberals and conservatives, Democrats and Republicans. That polarization creates gridlock, when it’s difficult to get legislation passed and policy problems addressed.

But just how polarized are they? We haven’t been able to tell in the past, because we haven’t been able to determine just how liberal or conservative state legislators are in all 50 states. One major reason why is that each state in its own way is rather unique. Massachusetts Republicans aren’t the same as Texas Republicans; the same is true for each state’s Democrats. Nor do they vote on the same things. These immutable differences mean that measuring  ideology–and levels of polarization–in state legislatures is much more difficult than that for Congress.

Nolan McCarty (Princeton University) and I wrote an academic paper in 2011 that explained our method for overcoming this problem. We have been working diligently since then to update our data, which we have released for free to the scholarly community and public here.

With our aggregate data in hand (and updated from our original estimates), we can begin to make precise comparisons between the states and Congress on a number of dimensions, including polarization. The plot below summarizes our measures for legislative polarization, averaging across all the years of our data (approximately 1996-2008), and across both legislative chambers (except for Nebraska).

The horizontal axis measures the amount of polarization, defined as the average ideological distance between the median of the Democratic and Republican parties in the state legislative chambers; larger numbers indicate more division. The dashed line is the level of Congressional polarization, included as a comparison (“US”).


What becomes immediately obvious is how different the states are from each other–and Congress–in terms of polarization. Some states, like Louisiana and Rhode Island, have quite unpolarized state legislatures. In Louisiana, both parties are fairly conservative, and in Rhode Island, they are both fairly liberal.

The state that sticks out like a sore thumb is my current home state, California. It is incredibly polarized; Democrats are extremely liberal, and Republicans are extremely conservative. In fact, California’s polarization is considerably larger than that in Congress (unlike Congress, however, Democrats dominate the state so thoroughly that this polarization is becoming increasingly toothless). This is also true for a number of other states.

All in all, polarization varies fairly dramatically across states.  The natural question is: why? Nolan McCarty and I–along with some coauthors–are engaged in a number of different research projects to try to answer that very question, as are a number of other scholars.

NB: We can measure Nebraska’s distance between party medians because, despite the fact that the Unicameral is officially nonpartisan, party affiliations of legislators are unofficially well known. We used friend and coauthor Seth Masket’s excellent Nebraska party data for that purpose.