Primary analysis involved genotypic effects on the main outcome variables AUDIT and smoking. Additive, dominant and recessive models of inheritance for the minor allele were all evaluated. Age and sex were included as covariates. Total sum of AUDIT items 1–10 was investigated using linear regression. Individuals smoking more than 10 cigarettes per day were grouped together and compared against the group that reported to be non‐smokers using logistic regression. Due to the fact that a large part of the present cohort consists of twins and siblings, gene‐dropping was used to maintain the between‐subjects dependence when evaluating the significance of the effects by repeated simulations (MacCluer et al. 1986).
