While smartphones have become promising tools for collecting digital behavioral, sensor, and survey data in the social sciences, the recruitment of study participants who are willing to install a smartphone app and fully participate throughout the study period remains a challenge. Previous research has experimented with various approaches to increase study participation and adherence, but with moderate success at most. In this paper, we report the results from qualitative in-depth interviews to better understand the mechanisms underlying the decision to participate in smartphone app data collection. The interviews are supported by a semi-structured discussion guide and conducted among individuals with different sociodemographic characteristics (age, gender, educational attainment) and varying levels of smartphone skills. The study aims to address the following questions: • Which potential difficulties and risks do individuals perceive in smartphone-based data collection? How do individuals perceive the collection of different forms of data, in particular survey, GPS, Internet browsing, and app usage data? • Under which conditions might individuals be more willing to participate and adhere in smartphone-based research? • Which strategies to increase participation and adherence might work best for whom? Which strategies might work best for underrepresented groups?
