Association of baseline e-cigarette ever use and covariates to combustible tobacco use outcomes at 6 and 12-month follow-ups among baseline never smokers
| Baseline regressors and covariates | Outcome | |||||||||
| Any tobacco product | Combustible cigarettes | Cigars | Hookah | Number of tobacco products | ||||||
| OR (95% CI)* | P value | OR (95% CI)* | P value | OR (95% CI)* | P value | OR (95% CI)* | P value | OR (95% CI)† | P value | |
| Unadjusted models | ||||||||||
| E-cigarette ever (vs never) use | ||||||||||
| Smoking outcome at 6 months | 3.76 (2.12 to 6.65) | <0.001 | 4.00 (2.07 to 7.71) | <0.001 | 3.99 (1.62 to 9.86) | 0.003 | 5.52 (2.74 to 11.12) | <0.001 | 3.90 (2.22 to 6.85) | <0.001 |
| Smoking outcome at 12 months | 11.39 (6.04 to 21.50) | <0.001 | 9.70 (5.12 to 18.37) | <0.001 | 3.99 (1.62 to 9.86) | 0.003 | 5.52 (2.74 to 11.12) | <0.001 | 8.40 (4.64 to 15.21) | <0.001 |
| Time (12 vs 6 months): e-cigarette never | 1.98 (1.41 to 2.78) | <0.001 | 2.43 (1.60 to 3.70) | <0.001 | 1.53 (0.73 to 3.17) | 0.26 | 2.01 (1.20 to 3.36) | 0.008 | 2.00 (1.43 to 2.82) | <0.001 |
| Time (12 vs 6 months): e-cigarette ever | 6.00 (2.98 to 12.11) | <0.001 | 5.89 (2.79 to 12.44) | <0.001 | 1.53 (0.73 to 3.17) | 0.26 | 2.01 (1.20 to 3.36) | 0.008 | 4.32 (2.15 to 8.70) | <0.001 |
| Ever e-cigarette use × time‡ | 3.03 (1.39 to 6.63) | 0.006 | 2.43 (1.07 to 5.48) | 0.033 | 1.44 (0.25 to 8.47) | 0.69 | 1.59 (0.48 to 5.24) | 0.45 | 2.15 (1.01 to 4.58) | 0.046 |
| Adjusted models | ||||||||||
| Categorical covariates | ||||||||||
| Girls (vs boys) | 0.94 (0.68 to 1.30) | 0.73 | 0.93 (0.65 to 1.33) | 0.69 | 0.65 (0.31 to 1.38) | 0.27 | 0.90 (0.53 to 1.54) | 0.71 | 0.92 (0.67 to 1.27) | 0.63 |
| Dutch (vs other) ethnicity | 0.42 (0.22 to 0.79) | 0.007 | 0.65 (0.31 to 1.37) | 0.26 | 0.55 (0.16 to 1.88) | 0.34 | 0.22 (0.08 to 0.55) | 0.001 | 0.42 (0.23 to 0.78) | 0.006 |
| Lives with both parents (vs other) | 0.86 (0.59 to 1.25) | 0.42 | 0.92 (0.63 to 1.36) | 0.69 | 0.75 (0.35 to 1.63) | 0.47 | 0.95 (0.51 to 1.75) | 0.86 | 0.88 (0.62 to 1.26) | 0.48 |
| Substance ever (vs never) use | 1.73 (1.21 to 2.47) | 0.002 | 1.74 (1.16 to 2.61) | 0.007 | 1.62 (0.74 to 3.56) | 0.23 | 1.54 (0.84 to 2.83) | 0.16 | 1.68 (1.18 to 2.40) | 0.004 |
| Family history of smoking (yes vs no) | 0.93 (0.67 to 1.29) | 0.66 | 0.93 (0.64 to 1.34) | 0.68 | 0.61 (0.28 to 1.31) | 0.20 | 0.86 (0.49 to 1.50) | 0.59 | 0.93 (0.66 to 1.32) | 0.69 |
| Continuous covariates§ | ||||||||||
| Age | 1.13 (0.96 to 1.34) | 0.14 | 1.18 (0.97 to 1.42) | 0.10 | 1.10 (0.75 to 1.63) | 0.62 | 1.08 (0.81 to 1.43) | 0.51 | 1.13 (0.96 to 1.34) | 0.15 |
| Parental education | 1.00 (0.85 to 1.19) | 0.96 | 1.04 (0.88 to 1.23) | 0.65 | 0.78 (0.54 to 1.12) | 0.17 | 1.10 (0.85 to 1.43) | 0.46 | 1.01 (0.86 to 1.17) | 0.95 |
| Peer smoking | 1.11 (0.96 to 1.27) | 0.17 | 1.09 (0.94 to 1.25) | 0.26 | 1.03 (0.77 to 1.37) | 0.85 | 1.12 (0.91 to 1.39) | 0.28 | 1.09 (0.96 to 1.25) | 0.17 |
| CESD-Depressive symptoms | 1.06 (0.91 to 1.24) | 0.47 | 1.09 (0.91 to 1.29) | 0.35 | 1.05 (0.75 to 1.45) | 0.79 | 1.00 (0.80 to 1.25) | 1.00 | 1.07 (0.92 to 1.24) | 0.36 |
| TCI-Impulsivity | 0.90 (0.77 to 1.06) | 0.21 | 0.90 (0.76 to 1.06) | 0.20 | 0.70 (0.47 to 1.03) | 0.07 | 0.93 (0.73 to 1.17) | 0.53 | 0.89 (0.76 to 1.04) | 0.14 |
| Delinquent behaviour | 1.03 (0.89 to 1.20) | 0.65 | 1.04 (0.88 to 1.22) | 0.66 | 1.18 (0.93 to 1.50) | 0.17 | 1.15 (0.92 to 1.44) | 0.23 | 1.05 (0.91 to 1.21) | 0.53 |
| Smoking susceptibility | 1.27 (1.10 to 1.46) | 0.001 | 1.31 (1.13 to 1.52) | <0.001 | 1.17 (0.85 to 1.62) | 0.33 | 0.91 (0.71 to 1.17) | 0.47 | 1.22 (1.07 to 1.39) | 0.002 |
| Smoking expectancies | 0.96 (0.81 to 1.13) | 0.62 | 0.90 (0.76 to 1.07) | 0.22 | 1.14 (0.75 to 1.74) | 0.54 | 1.06 (0.81 to 1.39) | 0.68 | 0.97 (0.82 to 1.13) | 0.67 |
| Regressors | ||||||||||
| E-cigarette ever (vs never) use | ||||||||||
| Smoking outcome at 6 months | 1.89 (1.05 to 3.37) | 0.032 | 1.93 (0.98 to 3.79) | 0.058 | 1.92 (0.75 to 4.93) | 0.18 | 3.69 (1.75 to 7.77) | 0.001 | 2.04 (1.16 to 3.60) | 0.0124 |
| Smoking outcome at 12 months | 5.63 (3.04 to 10.42) | <0.001 | 4.58 (2.42 to 8.68) | <0.001 | 4.32 (2.40 to 7.76) | <0.001 | ||||
| Time (12 vs 6 months): e-cigarette never | 1.98 (1.41 to 2.79) | <0.001 | 2.44 (1.60 to 3.72) | <0.001 | 1.53 (0.73 to 3.17) | 0.26 | 2.01 (1.20 to 3.35) | 0.008 | 2.01 (1.43 to 2.83) | <0.001 |
| Time (12 vs 6 months): e-cigarette ever | 5.92 (2.95 to 11.87) | <0.001 | 5.82 (2.77 to 12.19) | <0.001 | 4.25 (2.12 to 8.55) | <0.001 | ||||
| Ever e-cigarette use × time‡ | 2.99 (1.37 to 6.50) | 0.006 | 2.38 (1.06 to 5.37) | 0.036 | 1.43 (0.25 to 8.36) | 0.69 | 1.58 (0.48 to 5.20) | 0.45 | 2.12 (1.00 to 4.49) | 0.051 |
All analyses include only never users of combustible tobacco products at baseline (n=2185).
*OR from repeated binary logistic regression model predicting respective outcome from baseline ever e-cigarette use status (yes/no) including school fixed effects.
†OR from repeated ordinal logistic regression model predicting respective outcome from baseline ever e-cigarette use status (yes/no) including school fixed effects, with the OR expressing the change in odds of being in a category with use of a certain amount of tobacco products versus being in a category with lower use (3 vs ≤2, ≥2 vs ≤1, ≥1 vs 0).
‡If interaction term is significant (p≤0.05) or marginally significant (p≤0.10), the effect of e-cigarette use is examined both at 6 and 12- month follow-ups, and the effect of time is examined both for never and ever users of e-cigarettes. If interaction term is not (marginally) significant, the effect of e-cigarette use is examined averaged across and is thus the same for both the 6 and 12-month follow-ups, and the effect of time is examined averaged across and is thus also the same for never and ever users of e-cigarettes.
§Continuous covariates rescaled (M=0, SD=1), such that the ORs indicate change in odds in the outcome associated with an increase in one SD unit on the covariate continuous scale.
CESD, Center for Epidemiologic Studies Depression Scale; TCI, Temperament and Character Inventory.