The increasing polarization of US politics has drawn a growing amount of attention from scholars, journalists, and the public. Concerns about increasing levels of partisan and ideological conflict have raised important questions about representativeness, accountability, and effectiveness of the American government.

Despite the level of attention, scholarly knowledge of the causes and consequences of polarization is limited. This sketchy understanding is especially true of research on the polarization of elected officials, which has focused almost exclusively on the US Congress. Although much important work has been done on polarization in that context, examination of the history of polarization in the House and Senate provides only a limited perspective on the causes of polarization and its effects.

State legislatures, however, are an almost ideal setting for studying political polarization. States vary not only with respect to opinions and attitudes of their citizens, but also with respect to the electoral and legislative contexts that might contribute to greater or lesser partisan conflict.

Yet such research on state politics has been hampered by two problems to date. First, the data on roll call voting--used in standard measures of polarization--are not generally available. Second, where such data are available, polarization measures are not comparable across states.

The investigators in this project propose a solution to both problems and create ideological measures of individual state legislators that are comparable over time, across states, and with the US Congress. These measures are in turn used to assess the level of polarization within each state legislature. Preliminary findings establish wide variation in the extent of polarization. Some states show very little ideological difference between the two parties, while others are marked by a pronounced ideological divide. The project also demonstrates that polarization has evolved differently over time in different states. While polarization has grown in most state legislatures, it has remained constant or diminished in others.

The intellectual merits of this proposal are twofold. First, existing measures of individual and aggregate ideological preferences will be substantially augmented and linked to district and state demographic and electoral data. Second, this project will support multiple studies applying the new measures to study longstanding political questions. These puzzles include the causes and consequences of polarization, the multiple relationships between citizens and representatives, and the institutional and ideological underpinnings of differing policy choices across the states.

The project makes several contributions. It will yield three publicly accessible datasets ranging over all 50 states: legislative roll call data, which is only available today for 1999-2000; estimates of legislator ideology; and measures of political polarization and ideological conflict. All three data sets have numerous uses for scholars, practitioners, journalists, and the public. Along the way, the project will advance the professionalization of graduate students who participate in the research projects. Finally, policymakers and journalists would acquire additional insight into the relationship between institutional reform and ideological conflict.

National Science Foundation (NSF)
Division of Social and Economic Sciences (SES)
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Brian Humes
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University of Chicago
United States
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