On the basis of the survey questionnaire, from which information on smoking status (i.e., never smoker, former smoker, occasional or light smoker, and habitual smoker) and CPD for the habitual smokers were drawn, three smoking-related phenotypes were defined: SI, SQ, and SC. Regarding SI, the first measure (called SI-1) was defined as a binary trait comparing “never smoked” and “having regular smoking experiences,” and the second measure (called SI-2) was defined as an ordinal trait with four categories: never, former, light, and habitual. Because the association results for these two SI measures appear to be similar, in this communication, we show them together under the SI phenotype. The SQ phenotype was defined as an ordinal trait with five categories (1–5) according to CPD: non-smoking, <10 CPD, 11 to 20 CPD, 21 to 30 CPD, and >31 CPD. Such assessment of SQ not only has been commonly used in the literature but also is the most productive in terms of positive findings [43]. Finally, the SC phenotype was defined as a binary trait comparing “former smoking” and “current smoking.”
