E-cigarette use and subsequent smoking initiation
| Association with smoking initiation | Participants | Number of studies | Risk difference (95% CI)# | OR (95% CI) | Certainty of evidence | Down rating |
| Full material | 89 076 | Unadjusted: 17 Adjusted: 20 | 0.22 (0.14–0.28) | Unadjusted OR: 4.68 (3.64–6.02) Adjusted OR: 3.37 (2.68–4.24) | Moderate (+++) | −1 risk of bias¶ |
| Short-term follow-up (≤12 months) | 64 016 | Unadjusted:13 Adjusted: 18 | 0.18 (0.14–0.23) | Unadjusted OR: 4.60 (4.01–5.29) Adjusted OR: 4.13 (3.16–5.40) | Moderate (+++) | −1 risk of bias¶ |
| Long-term follow-up (>12 months) | 31 265 | Unadjusted: 8 Adjusted: 6 | 0.25 (0.13–0.38) | Unadjusted OR: 4.71 (3.03–7.34) Adjusted OR: 2.84 (1.85–4.36) | Moderate (+++) | −1 risk of bias¶ |
| <18 years | 761 399 | Unadjusted: 13 Adjusted: 15 | 0.07 (0.04–0.10) | Unadjusted OR: 5.11 (3.89–6.72) Adjusted OR: 2.94 (2.49–3.48) | Moderate (+++) | −1 risk of bias¶ |
| ≥18 years | 18 438 | Unadjusted: 4 Adjusted: 4 | 0.16 (0.11–0.22) | Unadjusted OR: 3.04 (2.57–3.58) Adjusted OR: 3.19 (1.44–7.05) | Low (++) | −1 risk of bias¶ −1 material with several limitations+,§ |
#: calculated from unadjusted values; ¶: material with several deficits and limitations; +: indirectness, three out of five studies are performed on college students in the USA; §: the analysis is based on a limited number of studies.