ERO power (delta 1–3 Hz) from one of the leads, family type (multiplex alcohol family or community family), number of parents who smoke, gender, and scores on principal components 1 and 2 derived from the stratification analysis of the sample genome (see Section 6.2). The CHRM2 SNPs analyzed here, rs978437, rs7800170, rs1824024, rs2061174, and rs2350786 include the three most significant of those for alcohol dependence with comorbid drug dependence in Dick et al. (2007, Table 1) as well as two others that appear to be in a range of significance indicated by that table. From preliminary statistical screening of the genotypic distributions in the sample, a recessive model was employed which contrasted major allele homozygotes with those who were not. The electrophysiological phenotypes (EROs) used in the analysis were found to be significant in previous studies (Jones et al., 2006a; Kamarajan et al., 2006; Rangaswamy et al., 2007); these studies showed reduced amplitudes in alcoholics and in those offspring at high risk. The number of parents who smoke were selected in part because the Kaplan-Meier curves with different values showed considerable variation. (See Keyes et al. (2008) for a discussion of the effects of parental smoking on adolescent behavior).
