Smoking initiation was defined as the age at which the person began smoking regularly. The presence of ND was ascertained by the three measures most commonly used in the literature: CPD; the Heaviness of Smoking Index (HSI 0-6 scale), which includes CPD and smoking urgency (i.e., how soon after waking up does the subject smoke the first cigarette?); and the FTND (0-10 scale) (Heatherton et al. 1991). CPD in the MSTF sample is categorized CPD, as used in the KARE samples. A detailed description of the demographic and clinical characteristics of the MSTF sample is presented in Table 2.
