1, approximately 2 years after completion of Wave 1 interviews, to assess retest reliability of the interview. All twins from the target cohort (excluding those who had withdrawn from the study or whose parents had refused permission to re-contact the family), were contacted for Wave 4 interviews, which were conducted from 2002-2005. Mean ages at the time of Wave 1, 3, and 4 assessments were 15.5 (SD=2.4), 19.0 (SD=2.1), and 21.7 (SD=2.8), respectively. The ethnic composition of the sample used in the current analyses is 90.1% Caucasian, 9.9% African-American.
