Table 2

Relationships between cigarette and e-cigarette use: (A) cross-sectional relationships between baseline cigarette and e-cigarette use; (B) prospective relationships between cigarette use at 1-year follow-up and e-cigarette use at baseline among baseline never used cigarettes; (C) prospective relationships between cigarette use at 1-year follow-up and e-cigarette use at baseline among baseline used once or used to use cigarettes

Cigarette UseBaseline e-cigarette use
NeverTriedInfrequentFrequent
(1–2 times)(1/month–1/week)(>1/week)
n (%)n (%)n (%)n (%)
A. Cross-sectional relationships at baseline (n=2836)
 Never1743 (61.5)407 (14.4)40 (1.4)6 (0.2)
 Once90 (3.2)201 (7.1)57 (2.0)10 (0.4)
 Used to20 (0.7)59 (2.1)38 (1.3)22 (0.8)
 Rarely (<1/week)8 (0.3)15 (0.5)31 (1.1)19 (0.7)
 Occasional (1–6/week)1 (0.0)6 (0.2)20 (0.7)10 (0.4)
 Frequent (>6/week)5 (0.2)7 (0.2)6 (0.2)15 (0.5)
B. Longitudinal relationships for baseline never users of cigarettes (n=1726)
 Never1259 (72.9)211 (12.2)13 (0.8)1 (0.1)
 Once86 (5.0)65 (3.8)8 (0.5)0 (0.0)
 Used to smoke19 (1.1)19 (1.1)1 (0.1)1 (0.1)
 Rarely (<1/week)11 (0.6)12 (0.7)1 (0.1)0 (0.0)
 Occasional (1–6/week)5 (0.3)3 (0.2)2 (0.1)0 (0.0)
 Frequent (>6/week)3 (0.2)1 (0.1)3 (0.2)2 (0.1)
C. Longitudinal relationships for baseline triers of cigarettes (n=318)
 No change61 (19.2)131 (41.2)43 (13.5)14 (4.4)
 Escalation9 (2.8)38 (11.9)17 (5.3)5 (1.6)