Discrete time survival analysis (DTSA) (Singer and Willett, 1993; Willett and Singer, 1993; Rodriguez, 2007) was used to investigate the contribution of genetic variants in CHRM2, ERO power, and environmental factors to the onset of regular alcohol use and of alcohol dependence in adolescents and young adults, to deal with the first two items of investigation. DTSA provides age-specific measures for the effects associated with predictive variables. Additional statistical tests, including both genetic and endophenotypic independent variables, were used to link the onset of regular alcohol use to the onset of alcohol dependence, to deal with the third item of investigation. To deal with the fourth item, the same DTSA methodology as was used for the entire sample was applied to a behaviorally defined sub-sample, the definition of which is discussed subsequently (see 2.5.1). The results of the DTSA calculations suggested further investigation of age related changes in the genotypic distributions of those who became alcohol dependent. A further test was made to determine whether there was an effect of alcohol use on our endophentypic covariates.
