Table 1.

The proportions for all three groups: no e-cigarette use, e-cigarette-only use, and e-cigarette use with other addictive substances, by independent variables

Variables	Categories	Total		E-cigarette status past 30 days
				No use		Single use		Poly use
		n	%	n	%	n	%	n	%
Academic achievement*	A or B	4538	73.6	4284	94.4	69	1.5	185	4.1
	C or D	1629	26.4	1467	90.0	47	2.9	115	7.1
Close friend alcohol use	No	3046	49.4	2980	97.9	41	1.3	25	0.8
	Yes	3121	50.6	2771	88.8	75	2.4	275	8.8
Close friend cigarette use	No	3882	62.9	3806	98.0	35	0.9	41	1.1
	Yes	2285	37.1	1945	85.2	81	3.5	259	11.3
Close friend other substance use	No	5501	89.2	5211	94.7	97	1.8	193	3.5
	Yes	666	10.8	540	81.0	19	2.9	107	16.1
Close friends persuade to use substance	No	5364	87.0	5120	95.4	84	1.6	160	3.0
	Yes	803	13.0	631	78.6	32	4.0	140	17.4
Sexual experience	No	5295	85.9	5060	95.5	84	1.6	151	2.9
	Yes	872	14.1	691	79.2	32	3.7	149	17.1
Household drug use	No	5150	83.5	4829	93.7	96	1.9	225	4.4
	Yes	1017	16.5	922	90.6	20	2.0	75	7.4
Sex	Male	2869	46.5	2607	90.0	77	2.7	185	6.4
	Female	3298	53.5	3144	95.3	39	1.2	115	3.5
Grade	8	2093	33.9	2008	95.9	32	1.5	53	2.5
	11	2052	33.3	1950	95.0	22	1.1	80	3.9
	Vocational	2022	32.8	1793	88.7	62	3.1	167	8.3

^*Academic achievement at A, B, C or D grade level.