Table 2 Estimated percentage point change in the mean prevalence of e-cigarette users among tobacco smokers who endorse the belief that e-cigarettes are less harmful than combustible cigarettes during the study period (2014–2019), based on autoregressive integrated moving average with exogenous input (ARIMAX) models stratified by age, sex and social grade
|  | 16–24 years | 25–64 years | 65+ years | |||
Unadjusted (95% CI,pvalue) | Adjusted (95% CI,pvalue) | Unadjusted (95% CI,pvalue) | Adjusted (95% CI,pvalue) | Unadjusted (95% CI,pvalue) | Adjusted (95% CI,pvalue) | |
Percentage change per 1% change in the mean prevalence of the exposure | ||||||
  Use of e-cigarettes | 0.12 (− 0.15–0.38), 0.39 | 0.13 (− 0.12–0.39), 0.31 | 0.42 (0.17–0.66), < 0.001 | 0.37 (0.13–0.61), < 0.01 | 0.22 (0.08–0.36), < 0.01 | 0.22 (0.07–0.37), < 0.01 |
  Current cigarette smokers | – | − 0.14 (− 0.38–0.10), 0.25 | – | 0.01 (− 0.23–0.24), 0.96 | – | − 0.03 (− 0.25–0.19), 0.78 |
  Tried to quit in the past year | – | 0.17 (− 0.08–0.43), 0.18 | – | 0.18 (− 0.07–0.42), 0.15 | – | − 0.11 (− 0.34–0.13), 0.37 |
  National mass media expenditure in millions (£) | – | − 0.11 (− 0.38–0.16), 0.43 | – | 0.16 (− 0.10–0.41), 0.23 | – | 0.08 (− 0.16–0.32), 0.50 |
Best fitting model | ||||||
  ARIMAX (p,d,q)(P,D,Q) | (0,1,1)(0,0,0) | (0,1,1)(0,0,0) | (0,1,1)(0,0,0) | (0,1,1)(0,0,0) | (0,1,1)(0,0,0) | (0,1,1)(0,0,0) |
  Non-seasonal (p value) |  |  |  |  |  |  |
   Autoregressive (AR) term | – | – | – | – | – | – |
   Moving average (MA) term | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 |
  Pseudo R2 | 0.02 | 0.08 | 0.17 | 0.23 | 0.28 | 0.29 |
| Â | Men | Women | Â | Â | ||
| Â | Unadjusted | Adjusted | Unadjusted | Adjusted | Â | Â |
Percentage change per 1% change in the mean prevalence of the exposure | ||||||
  Use of e-cigarettes | 0.42 (0.18–0.66), < 0.001 | 0.48 (0.18–0.78), < 0.01 | 0.21 (− 0.07–0.49), 0.14 | 0.13 (− 0.12–0.38), 0.29 |  |  |
  Current cigarette smokers | – | − 0.21 (− 0.44–0.02), 0.08 | – | 0.13 (− 0.08–0.34), 0.23 |  |  |
  Tried to quit in the past year | – | 0.18 (− 0.06–0.42), 0.15 | – | 0.37 (0.13–0.61), < 0.01 |  |  |
  National mass media expenditure in millions (£) | – | 0.27 (− 0.08–0.62), 0.13 | – | 0.08 (− 0.17–0.33), 0.52 |  |  |
Best fitting model | ||||||
  ARIMAX (p,d,q)(P,D,Q) | (0,1,1)(0,0,0) | (0,1,1)(0,0,0) | (0,1,1)(0,0,0) | (0,1,1)(0,0,0) |  |  |
  Non-seasonal (p value) |  |  |  |  |  |  |
   Autoregressive (AR) term | – | – | – | – |  |  |
   Moving average (MA) term | < 0.001 | < 0.001 | < 0.001 | < 0.001 |  |  |
  Pseudo R2 | 0.23 | 0.25 | 0.16 | 0.31 |  |  |
| Â | ABC1 | C2DE | Â | Â | ||
| Â | Unadjusted | Adjusted | Unadjusted | Adjusted | Â | Â |
Percentage change per 1% change in the mean prevalence of the exposure | ||||||
  Use of e-cigarettes | 0.50 (0.28–0.72), < 0.001 | 0.49 (0.27–0.71), < 0.001 | 0.43 (0.18–0.67), < 0.001 | 0.37 (0.12–0.61), < 0.01 |  |  |
  Current cigarette smokers | – | 0.06 (− 0.16–0.27), 0.59 | – | − 0.05 (− 0.28–0.18), 0.68 |  |  |
  Tried to quit in the past year | – | 0.06 (− 0.17–0.29), 0.61 | – | 0.28 (0.04–0.52), 0.02 |  |  |
  National mass media expenditure in millions (£) | – | 0.15 (− 0.08–0.38), 0.21 | – | 0.07 (− 0.19–0.32), 0.60 |  |  |
Best fitting model | ||||||
  ARIMAX (p,d,q)(P,D,Q) | (0,1,1)(0,0,0) | (0,1,1)(0,0,0) | (0,1,1)(0,0,0) | (0,1,1)(0,0,0) |  |  |
  Non-seasonal (p value) |  |  |  |  |  |  |
   Autoregressive (AR) term | – | – | – | – |  |  |
   Moving average (MA) term | < 0.001 | < 0.001 | < 0.001 | < 0.001 |  |  |
  Pseudo R2 | 0.27 | 0.30 | 0.19 | 0.27 |  |  |