Measurement Papers

The Ideological Mapping of American Legislatures

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

(Boris Shor and Nolan McCarty)

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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

(Boris Shor, Nolan McCarty, and Christopher Berry)

Published in the August 2010 issue of the Legislative Studies Quarterly

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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

(Boris Shor, 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)

Forthcoming in the American Journal of Political Science 

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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.


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.