Table 1.

Clinical characteristics of heavy, light, and never smokers.

	Heavy smokers(n = 70)	Light smokers(n = 209)	Never smokers(n = 209)
Age (years)	29.79 ± 3.05	29.27 ± 3.79	29.54 ± 3.41
Sex (M/F)	41/29	112/97	129/80
Education (years)	13.60 ± 1.87	14.49 ± 1.84	15.11 ± 1.74
Daily # drinks/prior year	3.26 ± 1.71	2.93 ± 1.71	2.98 ± 1.41
FTND score	4.83 ± 0.88	1.14 ± 1.11	/
Years of smoking	15.14 ± 3.34	13.00 ± 4.19	/
TIV (ccm)	1511 ± 209	1507 ± 176	1540 ± 182
Extn score	12.23 ± 8.74	10.06 ± 7.32	8.38 ± 6.36
Intn score	14.44 ± 12.56	10.34 ± 7.36	9.24 ± 8.59

Note: Values are mean ± SD. M: males; F: females. FTND scores > 6 were re-coded as 6. Years of smoking were re-coded as 5 (1–5 years), 10 (6–10 years), 15 (11–15 years), or 18 (16 + years). FTND scores and years of smoking were not available for never smokers. TIV: total intracranial volume; Extn: externalizing score; Intn: internalizing score. The three groups were matched in age, sex, and average daily number of drinks in the prior 12 months, but not in the years of education. Two-sample t tests showed significantly higher FTND scores (p < 0.001) and longer years of smoking (p < 0.001) in heavy smokers as compared to light smokers. The three groups did not differ in the TIV. With age, sex, years of education, and average daily number of drinks as covariates, univariate ANCOVA showed significant differences in the Extn (F = 5.63, p = 0.004) and Intn scores (F = 7.67, p = 0.001) across groups. Post-hoc multiple comparisons showed significantly higher Extn scores in heavy smokers as compared to never smokers (p = 0.005) and significantly higher Intn scores in heavy smokers than light smokers (p = 0.003) and never smokers (p’s < 0.001).