Table 2.
Final GEE model showing main effects of wave and image type, along with any significant interaction between wave and image type
| Outcomes, independent variables |
Canada | Australia | Mexico | ||||||
| est | 95% CI | P> z | est | 95% CI | P> z | est | 95% CI | P> z | |
| Noticing PHW, OR (95% CI) | |||||||||
| Survey wave | 0.019 | 0.528 | <0.001 | ||||||
| Wave 1 | ref | ref | ref | ||||||
| Wave 2 | 1.08 | (0.95 to 1.23) | 0.229 | n/a | 1.05 | (0.88 to 1.25) | 0.620 | ||
| Wave 3 | 1.26 | (1.09 to 1.47) | 0.002 | 1.12 | (0.92 to 1.37) | 0.258 | 1.20 | (1.00 to 1.44) | 0.056 |
| Wave 4 | 1.18 | (1.00 to 1.40) | 0.055 | 1.08 | (0.85 to 1.38) | 0.521 | 1.81 | (1.48 to 2.20) | <0.001 |
| Image type | <0.001 | 0.545 | 0.363 | ||||||
| Suffering | ref | ref | ref | ||||||
| Symbolic | 0.65 | (0.61 to 0.69) | <0.001 | n/a | n/a | ||||
| Graphic | 0.70 | (0.66 to 0.74) | <0.001 | 0.98 | (0.91 to 1.05) | 0.545 | 0.95 | (0.86 to 1.06) | 0.363 |
| Wave × image interaction | 0.027 | ||||||||
| Wave 2 × symbolic | n/a | n/a | n/a | ||||||
| Wave 2 × graphic | n/a | n/a | 0.92 | (0.80 to 1.05) | 0.219 | ||||
| Wave 3 × symbolic | n/a | n/a | n/a | ||||||
| Wave 3 × graphic | n/a | n/a | 1.04 | (0.90 to 1.20) | 0.624 | ||||
| Wave 4 × symbolic | n/a | n/a | n/a | ||||||
| Wave 4 × graphic | n/a | n/a | 0.86 | (0.74 to 0.99) | 0.034 | ||||
| Negative affects, β (95% CI) | |||||||||
| Survey wave | 0.629 | 0.027 | 0.044 | ||||||
| Wave 1 | ref | n/a | ref | ||||||
| Wave 2 | 0.06 | (−0.08 to 0.20) | 0.384 | ref | 0.00 | (−0.14 to 0.15) | 0.950 | ||
| Wave 3 | 0.08 | (−0.11 to 0.28) | 0.402 | 0.22 | (0.03 to 0.40) | 0.021 | −0.06 | (−0.24 to 0.13) | 0.550 |
| Wave 4 | 0.03 | (−0.23 to 0.28) | 0.837 | 0.36 | (0.09 to 0.63) | 0.009 | −0.25 | (−0.47 to 0.02) | 0.031 |
| Image type | <0.001 | <0.001 | <0.001 | ||||||
| Suffering | ref | ref | ref | ||||||
| Symbolic | −0.85 | (−0.90, to 0.80) | <0.001 | n/a | n/a | ||||
| Graphic | 0.49 | (0.45 to 0.52) | <0.001 | 0.22 | (0.17 to 0.27) | <0.001 | 0.33 | (0.29 to 0.35) | <0.001 |
| Believability, β (95% CI) | |||||||||
| Survey wave | 0.812 | 0.162 | 0.247 | ||||||
| Wave 1 | ref | n/a | ref | ||||||
| Wave 2 | 0.01 | (−0.14 to 0.17) | 0.868 | ref | −0.10 | (−0.24 to 0.04) | 0.177 | ||
| Wave 3 | 0.04 | (−0.18 to 0.26) | 0.722 | 0.15 | (−0.06 to 0.36) | 0.155 | −0.09 | (−0.25 to 0.08) | 0.301 |
| Wave 4 | −0.04 | (−0.31 to 0.24) | 0.787 | 0.29 | (−0.01 to 0.56) | 0.057 | −0.18 | (−0.38 to 0.01) | 0.064 |
| Image type | <0.001 | <0.001 | <0.001 | ||||||
| Suffering | ref | ref | ref | ||||||
| Symbolic | −0.65 | (−0.74 to 0.56) | <0.001 | n/a | n/a | ||||
| Graphic | −0.43 | (−0.51 to 0.35) | <0.001 | −0.22 | (−0.30 to 0.14) | <0.001 | −0.24 | (−0.28 to 0.21) | <0.001 |
| Wave × image interaction | 0.039 | 0.012 | |||||||
| Wave 2 × symbolic | 0.00 | (−0.12 to 0.12) | 0.998 | n/a | n/a | ||||
| Wave 2 × graphic | 0.02 | (−0.08 to 0.13) | 0.677 | n/a | n/a | ||||
| Wave 3 × symbolic | 0.07 | (−0.05 to 0.19) | 0.254 | n/a | n/a | ||||
| Wave 3 × graphic | 0.03 | (−0.08 to 0.13) | 0.645 | 0.09 | (−0.01, 0.19) | 0.092 | n/a | ||
| Wave 4 × symbolic | 0.15 | (0.03 to 0.27) | 0.012 | n/a | n/a | ||||
| Wave 4 × graphic | 0.14 | (0.03 to 0.24) | 0.009 | 0.16 | (0.05 to 0.26) | 0.003 | n/a | ||
| Quit motivation, β (95% CI) | |||||||||
| Survey wave | 0.646 | 0.062 | 0.263 | ||||||
| Wave 1 | ref | n/a | ref | ||||||
| Wave 2 | 0.04 | (−0.12 to 0.20) | 0.630 | ref | 0.04 | (−0.12 to 0.20) | 0.624 | ||
| Wave 3 | 0.12 | (−0.09 to 0.34) | 0.264 | 0.21 | (0.00 to 0.43) | 0.052 | −0.03 | (−0.24 to 0.18) | 0.769 |
| Wave 4 | 0.08 | (−0.19 to 0.34) | 0.577 | 0.34 | (0.05 to 0.63) | 0.021 | −0.17 | (−0.42 to 0.09) | 0.195 |
| Image type | <0.001 | <0.001 | <0.001 | ||||||
| Suffering | ref | ref | ref | ||||||
| Symbolic | −0.96 | (−1.01 to 0.90) | <0.001 | n/a | n/a | ||||
| Graphic | −0.01 | (−0.05 to 0.03) | 0.478 | 0.18 | (0.12 to 0.23) | <0.001 | −0.07 | (−0.10, to 0.03) | <0.001 |
| Discussion about PHWs, OR (95% CI) | |||||||||
| Survey wave | 0.638 | 0.393 | 0.225 | ||||||
| Wave 1 | ref | ref | ref | ||||||
| Wave 2 | 0.85 | (0.65 to 1.11) | 0.224 | n/a | 1.12 | (0.95 to 1.32) | 0.172 | ||
| Wave 3 | 0.89 | (0.68 to 1.18) | 0.430 | 0.92 | (0.75 to 1.13) | 0.441 | 0.97 | (0.82 to 1.17) | 0.731 |
| Wave 4 | 0.96 | (0.73 to 1.27) | 0.792 | 0.84 | (0.65 to 1.08) | 0.172 | 1.06 | (0.89 to 1.27) | 0.518 |
| Image type | <0.001 | <0.001 | 0.004 | ||||||
| Suffering | ref | ref | ref | ||||||
| Symbolic | 0.83 | (0.67 to 1.01) | 0.063 | n/a | n/a | ||||
| Graphic | 1.41 | (1.20 to 1.65) | <0.001 | 0.53 | (0.46 to 0.61) | <0.001 | 0.94 | (0.90 to 0.98) | 0.004 |
| Wave × image interaction | 0.021 | 0.006 | |||||||
| Wave 2 × symbolic | 0.98 | (0.75 to 1.29) | 0.888 | n/a | n/a | ||||
| Wave 2 × graphic | 0.98 | (0.79 to 1.22) | 0.847 | n/a | n/a | ||||
| Wave 3 × symbolic | 0.97 | (0.72 to 1.30) | 0.842 | n/a | n/a | ||||
| Wave 3 × graphic | 0.87 | (0.69 to 1.09) | 0.232 | 1.05 | (0.87 to 1.26) | 0.634 | n/a | ||
| Wave 4 × symbolic | 1.04 | (0.78 to 1.38) | 0.795 | n/a | n/a | ||||
| Wave 4 × graphic | 0.70 | (0.57 to 0.88) | 0.002 | 1.33 | (1.10 to 1.61) | 0.004 | n/a | ||
Interaction and stratification models were adjusted. Adjustment variables include: age, sex, educational level, income level, quit intention in the next 6 months, quit attempt, Heaviness of Smoking Index, daily smoking status, time in sample and race (Canada only).
β, regression coefficient; est, estimate (in bold type when significant); GEE, generalised estimating equation; n/a, not applicable; PHW, pictorial health warnings.
Bold values indicate significant result.