ABSTRACT
In this chapter, the authors present systematic evidence that a large set of visible interest groups have extreme policy positions. They accomplish this by integrating their ratings with the roll call data. The combined analysis of the "votes" of interest groups, and of the choices of representatives and senators, leads to an important substantive conclusion: Interest groups, particularly labor unions and ideological groups of the Left and Right, are more extreme than members of Congress. The authors provide three important methodological results. First, they validate the earlier D-NOMINATE estimates of spatial positions. Second, the authors are able to make direct comparisons of the House and Senate results since the interest groups effectively "vote" in both houses. Third, they use the results to discuss whether interest group ratings, which are widely used in professional journals in economics and political science, fulfill their intended purpose of being reasonable measures of "liberalism/conservatism" or "ideology".
