Selection and Influence: Interest Groups and Congressional Voting on Trade Policy

Abstract

Studies of the effects of interest groups on congressional roll-call voting typically view party and ideology as competing factors and rely on a factoral model of interests or a sectoral model including only interest groups with a direct stake in the vote. We depart from that strategy in several ways. We define interest groups at the level of Standard Industrial Classification two-digit codes and observe the universe of interests. For 1979–90, we use measures of geographically and nongeographically based economic interests to estimate the representative's party and ideology. We also consider the factor endowments of individuals within a district to examine their impact on floor votes. We then investigate the influence of these interests on members' party affiliation and ideology, as well as a pool of five floor votes on foreign trade, using instrumental variables for party and ideology. Economic interests account for a substantial portion of the variance in all cases, and models that also include other explanatory variables are highly accurate in estimating floor votes.