Table 1.

Participant characteristics

Variable	Sample size	Total M (SD) or %	Males M (SD) or %	Females M (SD) or %	pa
Baseline age, in years	516	14.87 (1.80)	14.86 (1.77)	14.90 (1.84)	.83
Baseline PDS score	514	2.99 (0.71)	2.70 (0.65)	3.29 (0.64)	<.001
Sensation seekingb					<.001
Baseline	515	10.89 (2.63)	11.45 (2.44)	10.33 (2.69)
Year 1	490	10.84 (2.87)	11.46 (2.58)	10.21 (3.01)
Year 2	462	10.98 (2.88)	11.71 (2.48)	10.24 (3.07)
Alcohol use, year 1	490	16.33%	15.57%	17.07%
Average drinks, 24 hours	80	2.96 (2.16)	3.42 (3.56)	2.55 (1.65)	.18
Drinking days, 365 days	80	5.53 (6.52)	3.97 (3.58)	6.93 (8.14)	.31
Total drinks, 365 days	80	18.32 (24.94)	15.50 (21.27)	20.87 (27.86)	.73
Total binges, 365 days	80	1.69 (3.61)	1.21 (2.35)	2.12 (4.45)	.90
Alcohol use year 2	456	30.70%	29.8%	31.6%	.67
Average drinks, 24 hours	142	3.15 (2.00)	3.58 (2.21)	2.73 (1.69)	.01
Drinking days, 365 days	142	11.37 (15.07)	11.16 (14.24)	11.58 (15.92)	.87
Total drinks, 365 days	142	44.05 (65.06)	49.96 (74.33)	38.46 (54.83)	.29
Total binges, 365 days	142	4.85 (8.21)	4.96 (8.42)	4.74 (8.07)	.87
Frequency of marijuana use
Days baseline year, 365 days	15	2.13 (1.46)	1.91 (1.58)	2.75 (0.95)	.34
Days year 1, 365 days	60	16.70 (45.38)	15.63 (28.35)	18.20 (62.60)	.83
Days year 2, 365 days	103	33.78 (68.17)	32.65 (61.49)	35.06 (75.75)	.86
Number of cigarettes used
Days baseline year, 365 days	2	2.00 (1.4)	2.00 (1.4)	n.a.	n.a.
Days year 1, 365 days	21	24.30 (41.78)	34.33 (51.72)	10.92 (18.30)	.21
Days year 2, 365 days	31	197.07 (932.16)	23.24 (65.24)	46.78 (119.47)	.13
NAcc volume (mm3)c
Baseline	502	1,563.49 (258.15)	1,616.98 (262.17)	1,511.27 (243.55)	.17
Scanner (% Siemens)	516	32.40%	33.1%	31.7%	.694

Notes: PDS = Pubertal Development Scale; n.a. = not applicable; NAcc = nucleus accumbens.

^aSex differences determined by Student’s t test or chi-square test;

^bmeasured using the sensation-seeking subscale of the UPPS-P;

^csex differences controlling for intracranial volume and scanner.