The impact of variants on smoking behaviour was assessed by comparing the prevalence of alleles stratified by cigarette consumption (cigarettes per day, CPD) using the Cochran-Armitage test. We also used the Kruskall-Wallis test to analyse for differences in cigarette consumption stratified by genotype. To test for independent effect of variants on CPD, genotype frequencies in light and medium smokers were compared to frequencies in heavy smokers using multinomial logistic regression.
