Ideology and Interests in the Political Marketplace


  • I thank Sandy Gordon, Patrick Egan, Alex Herzog, James Hollyer, Benjamin Lauderdale, Jonathan Nagler, Keith Poole, Jonathan Wand, Boris Shor, and, especially, Howard Rosenthal for their helpful comments and suggestions. Previous versions of this article were presented at the annual meetings of the Midwest and American Political Science Associations, the St. Louis Area Methods Conference, and the Princeton CSDP Fall seminar, where I received valuable feedback. Ideal point estimates, accompanying R code, and other data are available for download at

Adam Bonica is Assistant Professor of Political Science, Stanford University, Encina Hall West, 616 Serra Street, Room 308, Stanford, CA 94305–6044 (


I develop a statistical method to measure the ideology of candidates and political action committees (PACs) using contribution data. The method recovers ideal points for incumbents that strongly correlate with ideological measures recovered from voting records, while simultaneously recovering positions for PACs, unsuccessful challengers, and open-seat candidates. As the candidate ideal points are estimated independently of voting records, they represent a useful new resource for testing models of legislative behavior. By incorporating nonideological covariates known to influence PAC contributions, the method also shows promise as a platform for furthering our understanding of PAC contribution behavior.