For decades, critics of pluralism have argued that the American interest group system exhibits a significantly biased distribution of policy preferences. We evaluate this argument by measuring groups’ revealed preferences directly, developing a set of ideal point estimates, IGscores, for over 2,600 interest groups and 950 members of Congress on a common scale. We generate the scores by jointly scaling a large dataset of interest groups’ positions on congressional bills with roll-call votes on those same bills. Analyses of the scores uncover significant heterogeneity in the interest group system, with little conservative skew and notable inter-party differences in preference correspondence between legislators and ideologically similar groups. Conservative bias and homogeneity reappear, however, when weighting IGscores by groups’ PAC contributions and lobbying expenditures. These findings suggest that bias among interest groups depends on the extent to which activities like PAC contributions and lobbying influence policymakers’ perceptions about the preferences of organized interests.

Since the 1990s, members of the US House have shifted resources away from legislative functions to representational activities. We reveal this decline using an original dataset constructed from 236,000 quarterly payroll disbursements by 1,090 member offices for 120,000 unique staff between the 103rd and 113th Congresses, as well as interviews with former members and staff in Congress. These data allow us to test two plausible alternative explanations, one rooted in the centralization of legislative power over time and the other in conservatives’ desires to contract government power. We show that the decline in legislative capacity is symmetrical between and consistent within both parties, contrary to expectations rooted in asymmetrical, ideological sabotage. Additionally, this divestment occurs within incumbent member offices over time, accelerates when new members replace incumbents, and persists when majority control changes. We conclude that competition over institutional control and centralization of legislative functions motivates declining legislative capacity among individual members.

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