Abstract
Interest groups seek to influence parliamentarians' actions by establishing exchange relationships. We scrutinize the role of exchange by investigating how interest groups impact parliamentarians' use of individual parliamentary instruments such as questions, motions, and bills. We utilize a new longitudinal dataset (2000-2015) with 524 Swiss parliamentarians, their 6342 formal ties to interest groups (i.e., board seats), and a variety of 23,750 parliamentary instruments across 15 policy areas. This enables us to show that interest groups systematically relate to parliamentarians' use of parliamentary instruments in the respective policy areas in which they operate-even when parliamentarians' time-invariant (fixed effects) and time-variant personal affinities (occupation, committee membership) to the policy area are accounted for. Personal affinities heavily moderate interest groups' impact on their board members' parliamentary activities. Moreover, once formal ties end, the impact of interest groups also wanes. These findings have implications for our understanding of how interest groups foster representation in legislatures.