Because parents were older than non-parent participants, were more likely to have ever had a drink, had higher levels on most measures of quantity and frequency of alcohol use, and had higher rates of endorsement of alcohol dependence and abuse symptoms, in addition to the analyses conducted on the full sample of ever-drinking participants as described above, we also conducted all analyses separately for ever-drinking parents and non-parents. The results of these analyses are described in Supplemental tables S1A. through S5B. Separate parent and non-parent results are consistent with results from the full sample, in that for neither sub-group did polymorphisms in GABA systems have any significant effect using any analytical method.
