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The National Longitudinal Study of Adolescent to Adult Health (Add Health) is a longitudinal study of a nationally representative sample of over 20,000 adolescents who were in grades 7-12 during the 1994-95 school year and have been followed for six waves of data collection to date, most recently in 2022-25. Over the years, Add Health has collected rich demographic, social, familial, behavioral, psychosocial, cognitive, and health survey data from participants and their parents; a vast array of contextual data from participants’ schools, neighborhoods, and geographies of residence; and in-home physical and biological data from participants, including genetic markers, blood-based assays, anthropometric measures, and medications. Ancillary studies have added even more data over the years. Data from the project are available in various forms and have been analyzed in thousands of publications in peer-reviewed journals.