Table 1.

Baseline characteristics (N = 12,470).

		Weighted		Unweighted
	%	95%CI	Number	N (%)
Age (mean, 95%CI)
	13.74	13.71–13.77	708,765	14.45 (14.42–14.49)
Gender
Male	52.37	51.43–53.32	371,209	6736 (54.02)
Female	47.63	46.68–48.57	337,556	5734 (45.98)
Type of school
Junior high school	64.71	63.87–65.53	458,613	5842 (46.85)
Senior high school	22.87	22.14–23.62	162,091	3032 (24.31)
Vocational high school	12.42	12.01–12.85	88,062	3596 (28.84)
Boarding in school
Yes	14.28	13.73–14.85	101,211	2821 (22.62)
No	85.72	85.15–86.27	607,554	9649 (77.38)
Residence
Local	66.29	65.38–67.19	469,857	8350 (66.96)
Non-local	33.71	32.81–34.62	238,909	4120 (33.04)
Monthly allowance
<200 RMB (<31.5 USD)	34.64	33.74–35.55	245,506	4206 (33.73)
200–599RMB (31.5-94.5USD)	41.37	40.44–42.30	293,192	5204 (41.73)
≥600 RMB (≥94.5 USD)	23.99	23.20–24.81	170,068	3060 (24.54)
School performance
Top 25%	61.19	60.29–62.09	433,705	6537 (52.42)
Average	26.47	25.67–27.28	187,603	3830 (30.71)
Bottom 25%	12.34	11.79–12.92	87,458	2103 (16.86)
Friends’ e-cigarette use
No	82.92	82.23–83.59	587,709	9908 (79.45)
Yes	17.08	16.41–17.77	121,057	2562 (20.55)
Parents’ e-cigarette use
No	90.25	89.67–90.80	639,690	11,271 (90.38)
Yes	9.75	9.20–10.33	69,075	1199 (9.62)
E-cigarette curiosity
No	81.72	80.99–82.43	579,207	10,020 (80.40)
Yes	18.28	17.57–19.01	129,559	2450 (19.60)
Traditional smoking status
Never	95.01	94.62–95.37	673,394	11,663 (93.53)
Ever	4.18	3.84–4.55	29,635	644 (5.16)
Current	0.81	0.68–0.96	5746	163 (1.31)
E-cigarette use
Never	98.44	98.22–98.63	697,680	12,184 (97.71)
Ever	1.06	0.90–1.25	7522	175 (1.40)
Current	0.50	0.41–0.62	3564	111 (0.89)