In the present replication cohort, ND was ascertained by the three measures most commonly used in the literature: SQ (as defined in the above section), the Heaviness of Smoking Index (HSI: 0-6 scale), which includes SQ and smoking urgency (i.e., how soon after waking up does the subject smoke the first cigarette), and the Fagerström Test for ND (FTND: 0-10 scale) (17). A detailed description of the demographic and clinical characteristics of the sample is presented in Table 1.
