Ideology and Extremism of Interest Groups: Evidence from Lobbyist Declarations in Three States

Abstract

What are the ideological positions of private interests? Valid measurements of interest group and legislator preferences on the same scale enable a closer examination of the role of private interests in the legislative process. In this paper, I exploit lobbying disclosure requirements in Iowa, Nebraska, and Wisconsin to provide a new measure of interest group ideology. These states' legislatures either permit or require lobbyists to declare their principals' positions on lobbied bills. I combine these data with roll call votes and candidate survey responses to estimate, via an item-response model, the ideal points of legislators and interest groups in the same space. Although the interest groups' position-based ideal points correlate strongly with contribution-based measures, there is more extremism in the former, which is primarily driven by conservative-leaning groups. In addition to providing a new measure of interest group ideology, the analysis suggests that private interests, including corporations and trade groups, cannot be ruled out as a source of partisan polarization.