Table 1.

Respondent characteristics of the study sample at baseline (n = 1,152) and comparison with those lost to follow-up who would have otherwise been excluded (n = 1,225)

	Study sample (n = 1,152)	Lost to follow-up and excluded (n = 1,225)	OR (95% CI)
Ever smoked	229 (19.88)	382 (31.18)	.55 (.45–.66)
Ever used e-cigarettes	132 (11.46)	297 (24.24)	.40 (.32–.51)
Female	620 (53.82)	564 (46.04)	1.37 (1.16–1.61)
Age
11–13	438 (38.02)	375 (30.61)
14–15	338 (29.34)	263 (21.47)	1.10 (.89–1.36)
16–18	376 (32.64)	587 (47.92)	.55 (.45–.66)
School performance (1–4, 4 = excellent), mean (SD)	3.05 (.8)	2.97 (.8)	1.11 (1.01–1.22)
Problem behavior (2–8, 8 = high), mean (SD)	2.93 (1.2)	3.30 (1.4)	.80 (.75–.86)
Monthly alcohol use	269 (23.35)	407 (33.22)	.61 (.51–.73)
Susceptible to smoking	146 (12.67)	151 (12.33)	.86 (.67–1.11)
Susceptible to using e-cigarettes	264 (22.92)	330 (26.94)	.63 (.52–.77)
Some friends smoke
No	371 (32.2)	279 (22.78)
Yes	727 (63.11)	894 (72.98)	.61 (.51–.73)
DK/NA	54 (4.69)	52 (4.24)	.78 (.52–1.18)
Some friends use e-cigarettes
No	684 (59.38)	526 (42.94)
Yes	399 (34.64)	620 (50.61)	.49 (.42–.59)
DK/NA	69 (5.99)	79 (6.45)	.67 (.48–.95)
At least one parent smokes	343 (29.77)	413 (33.71)	.83 (.70–.99)
At least one parent uses e-cigarettes	182 (15.8)	221 (18.04)	.85 (.69–1.06)
Sibling(s) smokes
No	918 (79.69)	935 (76.33)
Yes	127 (11.02)	191 (15.59)	.68 (.53–.86)
NA/DK	107 (9.29)	99 (8.08)	1.10 (.83–1.47)
Sibling(s) use e-cigarettes
No	992 (86.11)	1016 (82.94)
Yes	54 (4.69)	119 (9.71)	.46 (.33–.65)
NA/DK	106 (9.20)	90 (7.35)	1.21 (.90–1.62)
Public approve of smoking	33 (2.86)	62 (5.06)	.55 (.36–.85)
Public approve of e-cigarettes	43 (3.73)	90 (7.35)	.49 (.34–.71)

All data are unweighted. Significant associations (p < .05) are highlighted in bold.

N (%) of the samples are reported unless otherwise stated.