Replication Data for: Get Out The Volunteer: Encouraging Diverse Political Party Activism

Political parties in advanced democracies face a dual challenge: fewer citizens are willing to volunteer, and those who remain active are disproportionately older and male. This is troubling given the central role that volunteers play in campaigns and party processes. Whether party leaders can recruit a larger and more diverse activist base remains an open question. We partnered with a major party in the Netherlands and conducted two field experiments before the 2021 general and 2022 municipal elections, targeting over 35,000 party members. They randomized whether members received a personal call, an email, or both. Results show that calls—where members could voice their opinions—increased volunteer sign-up rates (83\% in study 1 and 361\% in study 2), especially among younger members. By contrast, emails had no effect. These findings clarify mixed evidence in the literature, suggesting that voice opportunities are key to expanding and diversifying the activist base.