under the age of 25 may have a much higher chance than older people to develop smoking behavior if exposed to cigarettes. Therefore, after excluding these younger subjects from our control group, the subjects in the group that may later develop smoking behavior due to exposure to cigarettes, if existing, may not be in large numbers. Hence, the potential misclassification problem caused by our control subject selection strategy may have only moderate effects to the overall results of our study. The robustness of our GWAS findings is supported by their replication in both the AA and FHS cohorts.
