Just as parties build coalitions as a response to electoral conditions and interest group coalitions form to maximize political leverage, parties and interest groups may choose to establish organizational ties and collaborate. Yet, surprisingly little is known about why some take the strategic decision to form enduring ‘coalitions’ whereas others engage in less regularized or no interaction. Acknowledging that ideological proximity stimulates the formation of strong party-interest group ties, we apply a resource exchange model to account for variation. We hypothesize that whilst the mutual provision of tangible resources (like votes, donations or access to government) is needed to effectively explain whether parties and groups choose to establish (formal) coalitions, the distribution favors parties due their relatively superior position as gatekeeper to public office. Using data from a novel organizational survey of parties and interest groups conducted simultaneously in multiple Western democracies (the PAIRDEM-project) we test these hypotheses, but also examine how institutional factors (like state party finance and competition from other parties/groups) may influence the demand for and value of specific resources.
