PROJECT SUMMARY/ABSTRACT In line with the funding goals of the National Institute of Mental Health and PAR-18-714, this application proposes a research project that investigates the relationship between smartphone use, social media needs, and depressive symptoms. College students today are suffering more than ever from depressive symptoms, finding it difficult to function, and risking chronic or recurrent disorders and longstanding morbidity. Despite the identification of various risk factors in the literature, the causal mechanisms are not well understood. Recent research suggests that excessive mobile screen time may be linked with depressive symptoms, as well as other physical, psychological, social, and neurological adverse consequences. The majority of published studies, however, occurred outside of the United States, used a cross-sectional study design, or focused solely on smartphone addiction as opposed to screen time, so a gap remains in our knowledge of the causal relationship between screen time and depression. This study will test if objective measures of mobile phone screen time, through the collection of submitted screenshots, app usage, and social media needs, are associated with change in depressive symptoms in a cohort of U.S. college students. At the end of this project, the research team will have: a) identified consistent patterns of objective measured mobile screen time, app usage, and social media needs; b) assessed associations between those patterns with existing levels of depressive symptoms in a cross- sectional analysis; and c) determined if those patterns are predictive of longitudinal changes in depressive symptoms. The use of objective screen time measures is an innovative, feasible, and less biased way to measure patterns of mobile screen use and app use among the U.S. college student population. Moreover, this will be the first prospective, observational study evaluating the association between mobile screen time and changes in depressive symptoms. Understanding relationships between patterns of screen time and depressive symptoms will allow clinicians and researchers in future NIH-funded studies to: 1) better, more objectively identify college students at high risk for depression; 2) develop further understanding of the role of mobile screen time in the etiology of depression; and 3) ultimately implement targeted mobile-health interventions to address college student depression. Further, undergraduate student research assistants involved in the study will gain firsthand experience implementing online data collection, executing a prospective cohort study, and applying intermediate and advanced statistical tests; they will also be authors on peer-reviewed manuscripts and present at relevant conferences.