conducted, Wave 3 retest interviews were administered to a subset of Wave 1 twin participants. (Data from Wave 2 twin interviews were not used in the current study, as they were more limited in scope.) Wave 4 interviews were conducted from 2002 to 2005. Wave 5 interviews were conducted between 2005 and 2008. Of the 4,638 twins identified from birth records, 80% completed the Wave 4 interview (n=3,787), the primary source of data for this study. The mean age of participants at Wave 4 was 21.7 (SD=2.8; range=18–29) years; 14.6% of participants self-identified as African-American, the remainder as European-American.
