Questions drawn from the National Longitudinal Study of Adolescent Health (Add Health, Resnick et al. 1997) were administered to youth every year between 7th and 11th grades to assess the initiation of problem behaviors. Youth were asked if they had ever had sexual intercourse (“When I say sexual intercourse, I mean when a male inserts his penis into a female’s vagina”), if they had smoked cigarettes, cigars, or used chewing tobacco or snuff, and if they had used alcohol (beer, wine, wine coolers and liquor) or illegal drugs (marijuana, cocaine, crack, inhalants, heroin, LSD, PCP, ecstasy, mushrooms, speed and other pills not prescribed by a physician). These responses were used to stratify the sample into three groups reflecting the timing of first initiation of each behavior, as follows. Very early initiation involved first intercourse, tobacco use, or substance use by grade 8, age 14. Early initiation involved first intercourse, tobacco use, or substance use by grade 10– 11, age 16–17. Later (or non-) initiation included all other youth. Pregnancy and STDs were scored dichotomously, “1” indicating that a girl had
