sample were thus classified as early onset smokers. Research suggests that age of smoking onset can be reliably assessed with retrospective assessments [41]. To compare distinct levels of nicotine dependence, FTND scores were dichotomized into low (FTND = 0–4) and high (FTND = 6–10) dependence [7]. An FTND score of 6 or higher identifies subjects with high nicotine dependence [42], while a score of “5” has an ambiguous relation with dependence [42]–[44]. Of the initial sample of 2827, 731 (26%) were assigned to the low dependence condition, 1556 (55%) were assigned to the high dependence condition and 540 (19%) had an intermediate score of 5.
