Ideology, Party and Opinion: Explaining Individual Legislator ACA Implementation Votes in the States (PDF)

Published September 2018 at State Politics and Policy Quarterly

Why do state legislators vote the way they do? Which influence is predominant: ideology, party, or public opinion? The implementation votes surrounding the Affordable Care Act (ACA) provides a unique setting to examine this question, as they make all three considerations highly salient. State roll call votes on ACA implementation were sometimes polarized and sometimes unexpectedly bipartisan. What accounts for the heterogeneity in individual legislator behavior on bills implementing the ACA at the state level? Using new data on legislator ideology and votes from 2011-2015, 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. Moreover, I show the influence of ideology is heterogenous by issue area and bill.

Geography, Uncertainty, and Polarization  (PDF)


(with Jonathan Rodden, Chris Warshaw, Chris Tausanovitch, and Nolan McCarty)

Published March 2018 at Political Science Research and Methods

Using new data on roll-call voting of U.S. state legislators and public opinion in their districts, we explain how ideological polarization of voters within districts can lead to legislative polarization. So-called “moderate” districts that switch hands between parties are often internally polarized: the ideological distance between Democrats and Republicans within these districts is often greater than the distance between liberal cities and conservative rural districts. We present a theoretical model in which intra-district ideological polarization makes candidates uncertain about the ideological location of the median voter, thereby reducing their incentives to offer moderate policy positions. We then demonstrate that among districts with similar median voter ideologies, the difference in legislative behavior between Democratic and Republican state legislators is greater in more ideologically heterogeneous districts. Our findings suggest that accounting for the subtleties of political geography can help explain the coexistence of a polarized legislature and a moderate mass public.

Has the Top Two Primary Elected More Moderates? (PDF)

(with Eric McGhee)

Published December 2017 at Perspectives on Politics

Party polarization is perhaps the most significant political trend of the past several decades of American politics. Many observers have pinned hopes on institutional reforms to reinvigorate the political center. The Top Two primary is one of the most interesting and closely-watched of these reforms: a radically open primary system that removes much of the formal role for parties in the primary election and even allows for two candidates of the same party to face each other in the fall. Here we leverage the adoption of the Top Two in California and Washington to explore the reform’s effects on legislator behavior. We find an inconsistent effect since the reform was adopted in these two states. The evidence for post-reform moderation is stronger in California than in Washington, but some of this stronger effect appears to stem from a contemporaneous policy change—district lines drawn by an independent redistricting commission—while still more might have emerged from a change in term limits that was also adopted at the same time. The results validate some claims made by reformers, but question others, and their magnitude casts some doubt on the potential for institutions to reverse the polarization trend.

Ideology and the Congressional Vote (PDF Version)

(with Jon C. Rogowski)

Published June 2016 at Political Science Research and Methods

Abstract: A large class of theoretical models posits that voters choose candidates on the basis of issue congruence, but convincing empirical tests of this key claim remain elusive. The most persistent difficulty is obtaining comparable spatial estimates for winning and losing candidates, as well as voters. We address these issues using candidate surveys to characterize the electoral platforms for winners and losers, and large issue batteries in 2008 and 2010 to estimate voter preferences. Questions that were answered by both candidates and citizens allow us to jointly scale these estimates. We find robust evidence that vote choice in congressional elections is strongly associated with spatial proximity. Individual-level and contextual variables commonly associated with congressional voting behavior condition the importance of spatial proximity for vote choice, yet ideological considerations still continue to play a substantial role in vote choice. Our results have important implications for theories of voter decision-making and electoral institutions.

Reform and Representation: Assessing California’s Top-Two Primary and Redistricting Commission

(with Thad Kousser and Justin Phillips)

PDF Version

Published November 2016 at Political Science Research and Methods

Abstract: Can electoral reforms such as an independent redistricting commission and the top-two primary create conditions that lead to better legislative representation?  We explore this question by presenting a new method for measuring a key indicator of representation – the congruence between a legislator’s ideological position and the average position of her district’s voters.  We do this by combining two cutting-edge methods: the joint classification of voters and political candidates on the same ideological scale using a common policy survey, along with multilevel regression and post-stratification to estimate the position of the average voter across many districts in multiple elections.  After describing and validating our approach, we use it to study the recent impact of electoral reforms in California.  We draw on the predictions of reforms and the logic of spatial voting to show how the Citizens Redistricting Commission and the top-two primary might lead to a better fit between the state’s voters and lawmakers.  Then, by comparing levels of congruence and other trends in elections before (2010) and after (2012) the implementation of reform, we show that California’s electoral experiments did not bring their hoped-for effects.  If anything, legislators strayed further from their district’s average voter in 2012.  In sum, this paper lays out a replicable, practical method of gauging legislative representation, and applies it to show that attempts to improve representation do not always bear fruit.

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


Google Scholar Page

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


Google Scholar Page

(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.


Party Competition, Party Polarization, and the Changing Demand for Lobbying in the American States

(with Virginia Gray, John Cluverius, Jeffrey Harden and David Lowery)

Published in American Politics Research 43:2 (March 2015)

Interest system density influences internal dynamics within interest organizations, how they lobby, and policy conditions. But how do political conditions influence interest system density? How does politics create demand for interest representation? We examine these questions by assessing how legislative party competition and ideological distance between parties in state legislatures affect the number of lobby groups. After stating our theoretical expectations, we examine 1997 and 2007 data on legislative competition and party polarization to assess their influence on system density. We find mixed results: Whereas politics slightly influenced the structuring of nonprofit interest communities, they seem to have not affected the structuring of for-profit interest communities or interest communities as a whole.


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)

Google Scholar Page

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.

Red State/Blue State Divisions in the 2012 Presidential Election

(with Avi Feller and Andrew Gelman)

Published February 2013 in The Forum

The so-called “red/blue paradox” is that rich individuals are more likely to vote Republican but rich states are more likely to support the Democrats. Previous research argued that this seeming paradox could be explained by comparing rich and poor voters within each state – the difference in the Republican vote share between rich and poor voters was much larger in low-income, conservative, middle-American states like Mississippi than in high-income, liberal, coastal states like Connecticut. We use exit poll and other survey data to assess whether this was still the case for the 2012 Presidential election. Based on this preliminary analysis, we find that, while the red/blue paradox is still strong, the explanation offered by Gelman et al. no longer appears to hold. We explore several empirical patterns from this election and suggest possible avenues for resolving the questions posed by the new data.

The Ideological Mapping of American Legislatures

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

(with Nolan McCarty)

Google Scholar Page

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

Google Scholar Page

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.


Rich state, poor state, red state, blue state: What’s the matter with Connecticut?

(with Andrew Gelman, Joseph Bafumi, and David Park)

Published in the Quarterly Journal of Political Science, November 2007

Slide Presentation

Abstract: For decades, the Democrats have been viewed as the party of the poor, with the Republicans representing the rich. Recent presidential elections, however, have shown a reverse pattern, with Democrats performing well in the richer blue states in the northeast and coasts, and Republicans dominating in the red states in the middle of the country and the south. Through multilevel modeling of individuallevel survey data and county- and state-level demographic and electoral data, we reconcile these patterns.

Furthermore, we find that income matters more in red America than in blue America. In poor states, rich people are much more likely than poor people to vote for the Republican presidential candidate, but in rich states (such as Connecticut), income has a very low correlation with vote preference.

Key methods used in this research are: (1) plots of repeated cross-sectional analyses, (2) varying-intercept, varying-slope multilevel models, and (3) a graph that simultaneously shows within-group and between-group patterns in a multilevel model. These statistical tools help us understand patterns of variation within and between states in a way that would not be possible from classical regressions or by looking at tables of coefficient estimates.

A Bayesian Multilevel Modeling Approach to Time Series Cross-Sectional Data

(with Joseph Bafumi, Luke Keele, and David Park)
Published in Political Analysis, Spring 2007

Abstract: The analysis of time series cross-sectional (TSCS) data has become increasingly popular in political science. Meanwhile, political scientists are also becoming more interested in the use of multilevel models. However, little work exists to understand the benefits of multilevel modeling when applied to TSCS data. We employ Monte Carlo simulations to benchmark the performance of a Bayesian multilevel model (BML) for TSCS data against popular models used in the literature. We use various diagnostics to analyze the performance of our approach relative to these techniques. Compared to the most commonly employed estimators for such data, we find that the Bayesian multilevel model is (1) equally unbiased on average, (2) considerably more efficient, and (3) reports higher quality standard errors. Moreover, the BML is more general and flexible, which offers researchers additional advantages for TSCS data.