In the statistical model as used for this dataset the covariates for the intercept included sex, family type (Alcoholic or Community; see section 2.1), genotype (using an additive model) and a genotype × sex interaction, consistent with other studies of human development (Widén et al., 2010; Cousminer et al., 2013), and the first two principal components from the stratification analysis of the genetic dataset, which correspond to genetic ancestry (Astle and Balding, 2009); the only covariate for the slope is sex. Family type was used as a covariate in the regression analysis to address the possible differential effects, either genetic or environmental, of family history with regard to alcohol use disorders. Weights for individuals were adjusted to account for multiple observations on single individuals and co-presence of sibs in each of the local linear regression calculations. Weights for multiple observations from the same individual in any single regression calculation were adjusted by dividing each weight by the sum of all the weights used in the calculation for that individual if the sum was greater than 1. Weights for sibs were
