Linkage disequilibrium (LD) between markers was analyzed with Haploview 38. Both SNPs were in Hardy-Weinberg equilibrium. To test for an association between the SNPs and Impulsiveness we applied a regression test implemented in MERLIN-1.1-alpha program that takes family relationships into account in the association test 39. First, since the scores on the Impulsiveness facet from the Neuroticism domain did not differ significantly across assessment waves, we composed a new dependent variable for the Impulsiveness facet by averaging the individual’s scores across the different data waves. Second, we analyzed the correlation between the Impulsiveness scores and percentage of alcohol dependence symptoms using Spearman’s correlation since the alcohol variable was not normally distributed. To test the association of GABRA2 SNPs and percentage of alcohol dependence symptoms, a Zero-Inflated Poisson Regression model was applied to account for the excessive number of zeros (240/448) using SAS. The Zero-inflated Poisson test includes all subjects. The zero-inflated Poisson regression generates two separate models and then combines them. First, a model is generated for the “certain zero” cases. Then, a Poisson model is generated to predict the
