To investigate the question of whether rs4952 reflected additional association between this region and nicotine dependence, we used a traditional logistic regression model. Nicotine dependence was the dependent variable, and rs4952 was the predictor of interest. The variant rs13273442 was included as a conditioning covariate, and variables representing dependence on alcohol, cocaine, and marijuana were included to account for comorbidity, along with sex and age quartiles.
