(a) Early regular alcohol use: drinking one or more drinks per month for six months in a row, prior to age 17; (b) Early regular cigarette smoking: smoking one day a week for at least 2 months in a row, prior to age 16; (c) Early sexual debut: first consensual sex, prior to age 16; (d) Early maturation: onset of menses, prior to age 12. (e) One or more symptoms of conduct disorder. (f) Childhood exposure to sexual abuse, prior to age 17. Analyses in the full sample were also adjusted for self-reported ethnicity (Black vs. White) and age (less than 22 years); as members of twin pairs are matched for ethnicity and age, this adjustment was not necessary in the within-pair comparisons.
