Logistic regression analyses were undertaken using JMP 7 software. Backward stepwise regression was performed with variables being eliminated from the model in an iterative process. CTQ scores and ethnic factor scores were therefore included as covariates in the final model if they had significant effects (the European factor had a significant effect on heroin addiction in most analyses). The interaction term was included in the final model when significant. Logistic regression models with nominal variables yielded likelihood ratio χ2 results. The Fit Least Squares method was performed to determine differences in CTQ scores between patients with substance dependence and controls.
