After the last adult assessment (wave 7), a subsample of 349 participants was invited to participate in a supplementary genetics study (sample size was restricted by limited funding). Priority of selection was given to individuals who had participated during both adolescence and young adulthood to maximize the ability to test developmental gene-environment (G × E) prospective relationships. As described below, nine cases were excluded due to invalid genotyping data, yielding a final sample of 340. Statistical comparisons were made between the 340 individuals who were included in this study and those who were not on the major variables used in this study (e.g., alcohol use, heavy drinking friends' alcohol use, age, marital status, racial/ethnic group). The two groups did not differ significantly on any of these variables. Thus, this study used data from waves 4-7 on the 340 participants who had both genetic and interview data (see Table 2 for descriptive statistics of sample).
