The ND of each smoker was ascertained by three of the measures used most commonly in tobacco research: Smoking Quantity (SQ; defined as the number of cigarettes smoked per day), the Heaviness of Smoking Index (HSI; 0-6 scale), and the Fagerström Test for ND score (FTND; 0-10 scale) (Heatherton and others 1991). The SQ provides a simple, quantified index of consumption (using a 0–3 point compressed format), whereas HSI includes one item addressing SQ and another assessing smoking urgency on awakening. The FTND score includes the HSI plus other indicators of behavioral propensity to smoke under various circumstances. Given the presence of overlap in the content of the three ND measures, there exist fairly robust correlations among them (r = 0.88 ~ 0.94) in both the AA and EA samples. The primary reasons for employing all three measures were that there is a lack of consensus regarding the best approach to assess ND as a phenotype and to permit maximum cross-referencing with previous studies of ND.
