The present analyses included 6,242 individuals from complete twin pairs (n=3121) in which both members of the pair had complete data for all substance use measures from the 1992 interview and for educational attainment from the 1987 questionnaire. In 1992, the mean age of respondents was 41.9 years (SD=2.7) and most were married (77%). Based on military record data, 94% of the respondents were Caucasian, with 6% being African-American and <1% being of another ethnicity.
