more drinks per week (p < .001) and were younger (p < .001) compared to those who completed the COGA Phase II assessment but were not included in the present study; however, they did not differ in terms of sex, educational attainment, and household income. About 79.1% of the COGA Phase II sample provided a DNA sample for genotyping. Those who provided a DNA sample did not differ significantly from those who did not in terms of alcohol use and social support (p > .05).
