How U.S. state legislatures are polarized and getting more polarized (in 2 graphs)

January 14, 2014

Boris Shor is an assistant professor at the Harris School of Public Policy in the University of Chicago.  This post is the sixth in our series on political polarization.  The first five posts were by Nolan McCartyFrances LeeSean Theriault, Sarah Binder. and Michele Swers. – Dan Hopkins

America’s state legislatures are polarized–just like Congress–between liberals and conservatives, Democrats and Republicans.

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 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 differences mean that measuring ideology–and levels of polarization–is much more difficult for state legislatures than for Congress.

Nolan McCarty and I have come up with a method for overcoming this problem. We have released the resulting data set for free to the scholarly community and public here. This post uses those data as well as even more recent data that are currently being cleaned and prepared for public release.  Thus, we can analyze polarization through 2013 in most states.

The graph below shows the 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 Nolan McCarty’s inaugural post in this series detailed at the federal level. 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.

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