Table 2. Prevalence of Cigarette Smoking at Follow-up by Baseline e-Cigarette Vaping in Overall Sample and by Baseline Smoking Status.
| Follow-up Smoking Status | Overall Samplea | Baseline Vaping Statusa | P Value | |||
|---|---|---|---|---|---|---|
| Never | Prior | Infrequent | Frequent | |||
| Frequency in overall sampleb | 3084 | 2075 | 730 | 133 | 146 | |
| Nonsmokers | 2933 (95.1) | 2043 (98.5) | 676 (92.6) | 114 (85.7) | 100 (68.5) | <.001c |
| Infrequent smokers | 77 (2.5) | 18 (0.9) | 30 (4.1) | 12 (9.0) | 17 (11.6) | |
| Frequent smokers | 74 (2.4) | 14 (0.7) | 24 (3.3) | 7 (5.3) | 29 (19.9) | |
| Heaviness in overall sampled | 3052 | 2054 | 723 | 130 | 145 | |
| 0 cigarettes per day | 2904 (95.2) | 2024 (98.5) | 666 (92.1) | 109 (83.9) | 105 (72.4) | <.001e |
| <1 cigarette per day | 66 (2.2) | 11 (0.5) | 29 (4.0) | 14 (10.8) | 12 (8.3) | |
| 1 cigarette per day | 34 (1.1) | 10 (0.5) | 11 (1.5) | 2 (1.5) | 11 (7.6) | |
| ≥2 cigarettes per day | 48 (1.6) | 9 (0.4) | 17 (2.4) | 5 (3.9) | 17 (11.7) | |
| Frequency in baseline nonsmokers | 2966 | 2059 | 702 | 112 | 93 | |
| Nonsmokers | 2872 (96.8) | 2034 (98.8) | 659 (93.9) | 100 (89.3) | 79 (85.0) | <.001c |
| Infrequent smokers | 55 (1.9) | 15 (0.7) | 27 (3.9) | 8 (7.1) | 5 (5.4) | |
| Frequent smokers | 39 (1.3) | 10 (0.5) | 16 (2.3) | 4 (3.6) | 9 (9.7) | |
| Frequency in baseline infrequent smokers | 63 | 9 | 18 | 15 | 21 | |
| Nonsmokers | 38 (60.3) | 5 (55.6) | 14 (77.8) | 11 (73.3) | 8 (38.1) | .09c |
| Infrequent smokers | 14 (22.2) | 2 (22.2) | 2 (11.1) | 3 (20.0) | 7 (33.3) | |
| Frequent smokers | 11 (17.5) | 2 (22.2) | 2 (11.1) | 1 (6.7) | 6 (28.6) | |
| Frequency in baseline frequent smokers | 55 | 7 | 10 | 6 | 32 | |
| Nonsmokers | 23 (41.8) | 4 (57.1) | 3 (30.0) | 3 (50.0) | 13 (40.6) | .83c |
| Infrequent smokers | 8 (14.6) | 1 (14.3) | 1 (10.0) | 1 (16.7) | 5 (15.6) | |
| Frequent smokers | 24 (43.6) | 2 (28.6) | 6 (60.0) | 2 (33.3) | 14 (43.8) | |
Data are expressed as No. or No. (%). The percentages reflect the proportion for the column by row grouping. Never-vaper was defined as a student who never used an e-cigarette at baseline; prior vaper, used e-cigarette but no vaping during past 30 days; infrequent vaper, used e-cigarettes 1-2 days during past 30 days; and frequent vaper, used e-cigarettes on 3 or more days during past 30 days.
Indicates the No. of days smoked during past 30 days (nonsmoker, 0 days; infrequent smoker, 1-2 days; frequent smoker, ≥3 days).
Calculated using the Spearman ρ test for linear association between 2 ordinal variables of vaping (never-vapers, 0; prior vapers, 1; infrequent vapers, 2; frequent vapers, 3) and smoking frequency (0, nonsmokers;1, infrequent smokers; 2, frequent smokers).
Indicates the No. of cigarettes per day on smoking days during the past 30 days.
Calculated using the Spearman ρ test for linear association between 2 ordinal variables of baseline vaping (0, never-vapers;1, prior vapers; 2, infrequent vapers; 3, frequent vapers) and smoking heaviness (0; 1, <1 cigarette; 2, a whole cigarette; 3, ≥2 cigarettes).