Descriptive Statistics at Baseline and Attrition Analysis
gives descriptive statistics for all never-smokers at baseline, for those lost to follow-up, and for the final analyzed sample of baseline never-smokers, allowing comparisons of differences due to attrition. Never-smokers lost to follow-up were significantly older; more often male; had lower scores on the family affluence scale; rated their school performance more poorly; had higher scores in sensation-seeking/rebelliousness; had more friends, siblings, and parents who smoked; and were more often recruited from schools in Poland or Iceland.
Descriptive sample statistics at baseline and attrition analysis
Smoking Initiation During the Observation Period
Overall, 17% of the sample initiated smoking during the observation period. The incidence rate was 6% in Iceland, 17% in Germany, 18% in UK, 20% in Italy, 22% in The Netherlands, and 23% in Poland, with significant pair-wise comparisons for Germany vs Poland (p<0.001); UK vs Poland (p=0.001); and Iceland vs all other countries (all five p-values <0.001). After adjustment for between-country age and gender differences, the only remaining significant difference in smoking initiation was between Iceland and all other countries (all five p-values <0.001). The predicted age- and gender-adjusted incidence rates were 6% for Iceland; 19% for Germany, Italy, and UK; 20% for Poland; and 21% for The Netherlands, respectively.
Exposure to Smoking in Movies
Overall, 71% of the total 655 movies included at least one tobacco occurrence, with a range of 0–423 and a mean of 28.5 occurrences per movie. On average, the analyzed sample had seen 20 (SD=9) of the 50 movies on their movie list, which translated into an estimated mean individual exposure to on-screen tobacco of 1560 (median=1269, SD=1169) occurrences with a range of 0–6429 occurrences, based on the extrapolation to the respective 250 movies. The highest exposure was found for Icelandic students (M=1942 occurrences); followed by Polish (M=1850); Italian (M=1548); Scottish (M=1538); Dutch (M=1209); and German students (M=1014).
Association Between Exposure to Smoking in Movies and Adolescent Smoking Initiation
shows the unadjusted and adjusted association between exposure to movie smoking and adolescent smoking initiation for each country, and in the overall sample. The curves illustrate a monotonic increasing relationship through the exposure range for each country. The intercepts illustrate the different initiation rates in the six countries. also reports the crude and adjusted IRRs associated with exposure to 1000 tobacco occurrences, overall and by country. There was a significant crude association between exposure to movie smoking and smoking onset in the overall sample and in each country model, with the highest risk increase in Iceland (50% higher smoking incidence per 1000 occurrences) and the lowest risk increase in Italy (15%).
Crude and adjusted association between exposure to movie smoking occurrences and adolescents’ smoking initiation
After adjustment for age, gender, family affluence, school performance, TV screen time, sensation-seeking/rebelliousness, and smoking in the social environment, exposure to movie smoking was still significantly related to smoking onset in the overall sample and in five of the six country-specific models (Germany, Iceland, The Netherlands, Poland, and UK).
Overall, the adjusted IRR was 1.13 (95% CI=1.08, 1.17, p<0.001) for each additional 1000 occurrences of movie smoking exposure. The strongest adjusted association was found in the Scottish sample (adjusted IRR = 1.21 per 1000 occurrences, 95% CI=1.09, 1.34, p<0.001); there was no adjusted association found for Italy (IRR = 1.03, 95% CI=0.93, 1.15, nonsignificant).
A sensitivity analysis was conducted by additionally controlling for the absolute numbers of movies a student reported having seen. The correlation between exposure to movie smoking and number of movies seen was r =0.77. Despite this high correlation, exposure to movie smoking was still associated with smoking onset (adjusted IRR = 1.11, 95% CI=1.04, 1.19, p=0.003), whereas number of movies seen was not (adjusted IRR = 1.05, 95% CI=0.98, 1.13, p=0.156). To have comparable IRRs in this analysis, both variables were parsed into quartiles, with IRRs indicating the risk of smoking onset for each quartile of movie smoking exposure and number of movies seen, respectively.