The Dual Impact of Smartphone App Usage Diversity on Quality of Life: The Moderating Roles of Age and Digital Literacy.

This study investigates how smartphone app usage diversity (SAUD)-defined as the breadth of applications individuals actively engage with-relates to quality of life, and how these effects are conditioned by age and digital literacy. Drawing on Uses and Gratifications Theory and Cognitive Load Theory, we conceptualize SAUD as having both beneficial and detrimental potential, depending on users' cognitive and demographic characteristics. Using cross-sectional, self-reported data from the annual nationwide surveys on smartphone overdependence in South Korea, we analyzed a final sample of 20,967 adults (48.4% male, 51.6% female; M_age = 46.0, SD = 13.7; age range 20-69). Results demonstrate that SAUD is positively associated with quality of life among younger and digitally literate users, but negatively associated among older adults and those with lower digital literacy, suggesting the presence of conditional effects. The hypothesized three-way interaction between SAUD, age, and digital literacy was not supported. These findings extend the literature by moving beyond simplistic time-based metrics of smartphone use, offering a more differentiated understanding of mobile technology's impact on well-being. Practically, the study highlights the need for tailored digital literacy programs and policy interventions that recognize demographic and cognitive diversity in technology engagement. Future research should incorporate longitudinal designs and objective behavioral data to further validate these insights.