Opting in but not Donating? Participation in a Google Search Data Donation Study during the 2025 German Federal Election

Data donation studies are increasingly used to enrich survey data with digital behavioral data, but evidence on who participates - and who does not - remains mixed and difficult to generalize. This study explores the potential of enriching an election survey with donated Google Search data during the 2025 German federal election. Using a Bivariate Probit Model with Partial Observability, we model participation as a two-stage process, examining both willingness to participate and actual completion. We further test whether explicitly naming Google in the invitation affects participation.In line with prior work, younger individuals were more likely to opt in and complete the study. Gender differences were limited to willingness, and no systematic variation by education was observed. Naming Google in the invitation affected willingness, but not completion. Notably, we examine participation by party vote, contributing to a better understanding of participation by political leaning. Voters of the Green Party were more willing to participate and together with FDP voters, also more likely to complete the donation, controlling for age, gender, and education. This may indicate a political skew in donated data, as these voter groups tend to be younger, more liberal, and possibly more trusting of science.