Strengths of this analysis include the prospective design and repeated sampling, which may minimize recall bias among participants. In addition, multiple imputation was used to manage missing data. Limitations include potential selection bias due to convenience sampling, restriction of the study population to Caucasians (to minimize population stratification), as well as genotyping for prevalent CYP2A6 alleles in Caucasians known to reduce CYP2A6 activity. The presence of undetected CYP2A6 alleles conferring slow nicotine metabolism may misclassify some individuals as normal or intermediate metabolizers, however this would likely reduce, rather than enhance, the likelihood of observing increased quitting among slow metabolizers.
