Political parties and interest groups play a vital role in incorporating societal interests into democratic decision-making. Because both organisational forms derive benefit from selective structured interactions with the other, explaining the nature and variation in these relationships will advance our understanding of democratic governance. Our contribution is to examine how system-level variables constrain parties’ structured interaction with interest groups. Specifically, we investigate whether the competitive situation on both sides affects the strength of relational ties. We assume fragmentation makes strong ties to particular groups less attractive and hypothesize that parties’ tend to have weaker relations to specific group categories when other parties compete for the same groups' support, and when there are other groups occupying the same policy space in the political debate. Controlling for, above all, group resources (size and party donations), party finance regime, state structure and historical legacy, the hypotheses are tested utilizing new data on 158 party units (central party organisations and legislative party groups) and 105 unique parties in 19 countries. Our results will have significant implications for the understanding of political parties, interest groups and democratic political systems more generally.
