The sample was drawn from 20,774 adolescents in the National Longitudinal Study of Adolescent Health (Add Health) database. Add Health is an ongoing, longitudinal study with a nationally representative sample of U.S. adolescents. Add Health participants have been followed from adolescence into adulthood via four waves of data collection. The Add Health study selected 80 U.S. high schools and 52 middle schools for study inclusion. These schools were selected through a stratified random sampling process that yielded a sample of schools that was representative of U.S. schools with respect to region, urbanicity, race/ethnicity, school type, and size. Some racial/ethnic groups were oversampled (e.g., middle-class African Americans). Wave 1 data were collected from 1994 to 1995, Wave 2 in 1996, Wave 3 from 2001 to 2002, and Wave 4 from 2007 to 2008. At Wave 1, the mean age of the participants was 15.65 years (SD =1.75) years; at Wave 2, the mean age was 16.22 years (SD = 1.64); at Wave 3, the mean age was 22.96 years (SD = 1.77); and at Wave 4, participant’s mean age was 28.9
