Table 1.

Descriptive statistics for all study variables.

Variable	Range	Mean (SD)/%, time 1	Mean (SD)/%, time 2
Coffee	1–7	1.63 (1.14)	1.58 (1.07)
Tea	1–7	2.52 (1.81)	2.40(1.70)
Caffeinated soda/pop	1–7	2.86 (1.83)	2.72 (1.73)
Energy drinks	1–7	1.39 (1.12)	1.38 (1.09)
Caffeine (weighted, non-transformed)	13–91	24.24 (13.00)	23.38 (12.22)
Caffeine (weighted, log-transformed)	2.56–4.51	3.09 (0.42)	3.06 (0.41)
Ever cigarette smoking (%)	0–1	6.4	8.1
Ever use of e-cigarettes (%)	0–1	5.9	10.3
Ever used alcohol (%)	0–1	8.8	14.4
Ever been drunk (%) Control variables	0–1	3.9	5.6
Girls (%)	0–1	49.8
Lives with both parents (%)	0–1	56.8
White (%)	0–1	77.4
Mother’s education	1–9	2.91 (2.46)

SD = standard deviation.