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Updated (July 2014) State Legislator Ideology Scores Posted

Yesterday I posted the aggregate, state-level ideology and polarization data for our state legislature ideology data. That is actually based on legislator-level data. Today, we are posting and making public and free that individual level data.

We have extended the data collection through 2013, and we now have 20,198 unique state legislators in our data, or about 11% more than the previous update from May 2013.

As I mentioned yesterday, we have spent 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.

New this year is a district-by-year indicator, as these legislators do change districts over time.

You can find the data here.

Bugs should be reported to us.


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.

Updated Aggregated Data Release

We are releasing a new version of our state and chamber-level aggregate data. We have focused on two major updates:

  1. In all, we have 140 chamber-years of new data. These now include party data for Nebraska thanks to friend and coauthor Seth Masket, who generously provided the informal but well-known partisan affiliations for Unicameral legislators.
  2. The individual level data underlying this release has been extensively cleaned to minimize the random noise inherent in acquiring roll call votes from printed journals.

You can find the data here.