population of Missouri, where approximately 14% of adolescents and young adults identify as African-American. In 2002–2005, all female twins from the target cohort (excluding those who had previously withdrawn from the study or whose parents had refused permission for the family to be re-contacted) were approached for follow-up (Wave 4) interviews. All women who completed Wave 4 assessments were subsequently invited to participate in the fifth wave of data collection, which began in 2005.
