Measurement Papers

The Ideological Mapping of American Legislatures

American Political Science Review (August 2011), 105:3, pp. 530-551.

(with Nolan McCarty)

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Data Download

Abstract: The development and elaboration of the spatial theory of voting has contributed greatly to the study of legislative decision making and elections. Statistical models that estimate the spatial locations of individual legislators have been a key contributor to this success (Poole and Rosenthal 1997, Clinton et al 2004). In addition to applications to the U.S. Congress, spatial models have been estimated for the Supreme Court, U.S. presidents, a large number of non-U.S. legislatures, and supranational organizations. But, unfortunately, a potentially fruitful laboratory for testing spatial theories of policymaking and elections, the American states, has remained relatively unexploited. Two problems have limited the empirical application of spatial theory to the states. The first is that state legislative roll call data has not yet been systematically collected for all states over time. Second, because ideal point models are based on latent scales, comparisons of ideal points across states or chambers within a state are difficult. This paper reports substantial progress on both fronts. First, we have obtained the roll call voting data for all state legislatures from the mid-1990s onward. Second, we exploit a recurring survey of state legislative candidates to enable comparisons across time, chambers, and states as well as with the U.S. Congress. The resulting mapping of America’s state legislatures has tremendous potential to address numerous questions not only about state politics and policymaking, but legislative politics in general.

A Bridge to Somewhere: Mapping State and Congressional Ideology on a Cross-Institutional Common Space

(with Nolan McCarty and Christopher Berry)

Published in the August 2010 issue of the Legislative Studies Quarterly

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Aggregate Replication Data Download


Researchers face two major problems when applying ideal point estimation techniques to state legislatures. First, longitudinal roll-call data are scarce. Second, even when such data exist, scaling ideal points within a single state is an inadequate approach. No comparisons can be made between these estimates and those for other state legislatures or for Congress. Our project provides a solution. We exploit a new comparative dataset of state legislative roll calls to generate ideal points for legislators. Taking advantage of the fact that state legislators sometimes go on to serve in Congress, we create a common ideological scale. Using these bridge actors, we estimate state legislative ideal points in congressional common space for 11 states. We present our results and illustrate how these scores can be used to address important topics in state and legislative politics.

Methodological Issues in Bridging Ideal Points in Disparate Institutions in a Data Sparse Environment

(with Nolan McCarty and Christopher Berry)

Working Paper

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Abstract: In earlier work, we created Congressional common space scores for multiple state legislatures using bridge actors who served in both institutions. Here, we employ simulations to explore the general issues involved in bridging institutions in data-sparse environments, where only a few bridge actors exist to allow inter-institutional comparisons. We find that only a few such bridges are necessary to improve ideal point estimates of rescaled legislative chambers.

Application Papers

A Primary Cause of Partisanship? Nomination Systems and Legislator Ideology

(with Eric McGhee, Seth Masket, Steven Rogers, and Nolan McCarty)

Published in the American Journal of Political Science (April 2014)

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Abstract: Many supporters of political reform advocate opening party nominations to non-members as a way of increasing the number of moderate elected officials. This presumes that the composition of the primary electorate is, in fact, a significant cause of polarization, an idea that has rarely been tested empirically. We marry a unique new data set of state legislator ideal points to a detailed accounting of primary systems to gauge the effect of primary systems on polarization. The results of this analysis suggest that the openness of a primary election has little effect, if any, on the partisanship of the politicians it produces. We speculate on why the effect is so inconsistent and weak, and discuss the implications of our study for the theoretical literature on parties in American political life.

Ideology, Learning, and Policy Diffusion: Experimental Evidence

(with Craig Volden, Dan Butler, and Adam Dynes)

Forthcoming in the American Journal of Political Science 

Accepted June 2015, Published online July 2015


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Abstract:   We introduce experimental research design to the study of policy diffusion in order to better understand how political ideology affects policymakers’ willingness to learn from one another’s experiences. Our two experiments–embedded in national surveys of U.S. municipal officials–expose local policymakers to vignettes describing the zoning and home foreclosure policies of other cities, offering opportunities to learn more. We find that: (1) policymakers who are ideologically predisposed against the described policy are relatively unwilling to learn from others, but (2) such ideological biases can be overcome with an emphasis on the policy’s success or on its adoption by co-partisans in other communities. We also find a similar partisan based bias among traditional ideological supporters, who are less willing to learn from those in the opposing party. The experimental approach offered here provides numerous new opportunities for scholars of policy diffusion.


Polarization without Parties: Term Limits and Legislative Partisanship in Nebraska’s Unicameral Legislature


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(with Seth Masket)

Published in the State Politics and Policy Quarterly (March 2015)

Abstract: Despite a long history of nonpartisanship, the Nebraska state legislature has polarized rapidly within the past decade. Using interviews and campaign finance records, we examine politics in the modern Unicam to investigate nonpartisan polarization. We find that newly-instituted term limits created opportunities for the state’s political parties to recruit and finance candidates in an increasingly partisan fashion. Social network analysis suggests that there is a growing level of structure to campaign donations, with political elites increasingly less likely to contribute across party lines. The results offer a compelling example of parties overcoming institutions designed to eliminate them.

Unequal Incomes, Ideology and Gridlock: How Rising Inequality Increases Political Polarization

(with John Voorheis and Nolan McCarty)

Working Paper

Income inequality and political polarization have both increased dramatically in the United States over the last several decades. A small but growing literature has suggested that these two phenomena may be related and mutually reinforcing: income inequality leads to political polarization, and the gridlock induced by polarization reduces the ability of politicians to alleviate rising inequality. Scholars, however, have not credibly identified the causal relationships. Using newly available data on polarization in state legislatures and state-level income inequality, we extend previous analyses to the US state level. Employing a relatively underutilized instrumental variables identification strategy allows us to obtain the first credible causal estimates of the effect of inequality on polarization within states. We find that income inequality has a large, positive and statistically significant effect on political polarization. Economic inequality appears to cause state Democratic parties to become more liberal. Inequality, however, moves state legislatures to the right overall. Such findings suggest that the effect of income inequality impacts polarization by replacing moderate Democratic legislators with Republicans.

Primary Electorates vs. Party Elites: Who are the Polarizers?

(with Seth Masket)

Working Paper

Advocates of direct primaries argued that party nominees selected by voters should be more independent-minded than those hand-selected by party elites. We test this claim through a study of state legislative vacancy appointments, through which a small group of party activists is responsible for replacing legislators who have died or resigned. We compare the roll call voting behavior of two decades of legislators in Colorado and Illinois based on whether the legislators were directly nominated in primary elections or selected by party elites on a partisan vacancy committee. Results demonstrate that there is, in fact, little ideological difference between the two types of incumbents, suggesting that party elites are largely able to secure the nominations of their preferred candidates even under conditions of a direct primary.

Individual ACA Implementation Votes in the States on State Insurance Exchanges and Medicaid Expansion

Working Paper

The Affordable Care Act (ACA) makes states central in health insurance reform to an astounding degree. The centerpiece of state-level policy choices are the state-based health insurance exchanges and the state-level decisions on whether to expand Medicaid.While many states avoided votes on these two, where states did vote, roll call votes were typically highly controversial and polarized. What accounts for the heterogeneity in individual legislator behavior on bills implementing the ACA at the state level? I show evidence that legislator ideology was by far the most important predictor of voting on implementation votes, far more so than legislator party or public opinion.

The Causes and Consequences of Party Switching in American State Legislatures

Working Paper

Abstract: The influence of parties is a perennial topic for debate. Do parties affect their member’s revealed preferences, or do they merely reflect them? Attempts to isolate party effects are fraught with inference problems. Using the natural experiment afforded by legislators switching parties, previous studies such as \cite{Nokken:2000, Nokken:2004} measure preference shifts. Assuming personal preferences to be constant, these shifts are held to reflect party pressure. The problem is that, due to the focus on Congress, only a miniscule number of modern cases exist, and institutional variation is minimal. Consequently, inferences drawn are not as strong. We use a new, original data set of state legislator ideology in 50 states from 1993-2008, drawing from roll call votes and legislator surveys. These ideal point estimates are in common space for cross-state comparability. We find nearly 170 party switchers at the state level, dwarfing by nearly five times that for postwar Congresses. We analyze the degree of ideological change revealed by party switchers, as well as their incidence.


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