BackgroundIn Western countries, smoking accounts for a large share of socio-economic inequalities in health. As smoking initiation occurs around the age of 13, it is likely that school context and social networks at school play a role in the origin of such inequalities. So far, there has been little generic explanation of how social ties at school contribute to socio-economic inequalities in smoking. The SILNE (Smoking Inequalities – Learning from Natural Experiments) survey was designed to test the hypothesis that a combination of peer effect, homophilous social ties, and school context may explain how smoking inequalities are magnified at school – a theory known as network-induced inequality. In this paper, the survey theory and design are presented.FindingsThe social network survey was carried out in 2013 in six medium-sized European cities with average incomes similar to the national average: Namur (Belgium), Tampere (Finland), Hannover (Germany), Latina (Italy), Amersfoort (The Netherlands), and Coimbra (Portugal). In each city, 6 to 8 schools were selected in a stratified sampling procedure. In each school, two grades in secondary education, corresponding to 14-16-year-olds, were selected. All adolescents in these two grades were invited to participate in the survey. Social ties were reported using the roster approach, in which each adolescent had to nominate up to 5 friends from a directory.The survey collected information from 11,015 adolescents in 50 schools, out of a total of 13,870 registered adolescents, yielding a participation rate of 79%. The SILNE survey yielded 57,094 social ties, 86.7% of which referred to friends who also participated in the survey.DiscussionThe SILNE survey was designed to measure the association between adolescents’ social ties at school, their socio-economic background, and their smoking behaviour. Two difficulties were encountered, however: legal privacy constraints made it impossible to apply the same parental consent procedure in all countries, leading to somewhat lower participation rates in two cities: Hannover and Latina. It was also difficult to match the 6 cities in terms of both age and type of education.The SILNE survey provided a comparable database for the study of smoking inequalities across European cities from a social network perspective.Electronic supplementary materialThe online version of this article (doi:10.1186/s13104-015-1041-z) contains supplementary material, which is available to authorized users.

ObjectivesSmoking contributes to socio-economic health inequalities; but it is unclear how smoking inequalities emerge at a young age. So far, little attention has been paid to the role of friendship ties. We hypothesised that the combination of peer exposure and friendship social homophily may contribute to socio-economic inequalities in smoking at school.MethodsIn 2013, a social network survey was carried out in 50 schools in six medium-size European cities (Namur, Tampere, Hanover, Latina, Amersfoort, and Coimbra). Adolescents in grades corresponding to the 14-to-16 age group were recruited (n = 11.015, participation rate = 79.4 %). We modelled adolescents’ smoking behaviour as a function of socio-economic background, and analysed the mediating role of social homophily and peer exposure.ResultsLower socio-economic groups were more likely to smoke and were more frequently exposed to smoking by their close and distant friends, compared with adolescents of higher SES. The smoking risk of the lowest socio-economic group decreased after controlling for friends smoking and social homophily.ConclusionsSmoking socio-economic inequalities amongst adolescents are driven by friendship networks.Electronic supplementary materialThe online version of this article (doi:10.1007/s00038-016-0830-z) contains supplementary material, which is available to authorized users.

Poor academic performance is a known risk factor for adolescent smoking, yet the association remains unclear, as the role of social ties has been rarely examined. Our study aims to investigate the role of friendship ties in this association. In a sample of 11,015 adolescents, aged 14 to17, in 50 schools within six European cities (SILNE-survey, 2013), we used multilevel models to analyse the mediating effect of the composition of friendship ties and school types on the association between academic performance and smoking. Results show smoking was more prevalent in adolescents with lower academic performance than with higher. This association was stronger in non-vocational schools than in vocational. Adolescents tended to have friendship ties with someone sharing the same smoking status and academic performance. Finally, friendship networks are patterned both on smoking and academic performance. This suggests the educational environment contributes to future socioeconomic inequalities in smoking among young people.

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BackgroundAlthough there is evidence for socioeconomic inequalities in health and health behaviour in adolescents, different indicators of socioeconomic status (SES) have rarely been compared within one data sample. We examined associations of five SES indicators with self-rated health (SRH) and smoking (ie, a leading cause of health inequalities) in Europe.MethodsData of adolescents aged 14–17 years old were obtained from the 2013 SILNE survey (smoking inequalities: learning from natural experiments), carried out in 50 schools in 6 European cities (N=10 900). Capturing subjective perceptions of relative SES and objective measures of education and wealth, we measured adolescents’ own SES (academic performance, pocket money), parental SES (parental educational level) and family SES (Family Affluence Scale, subjective social status (SSS)). Logistic regression models with SRH and smoking as dependent variables included all SES indicators, age and gender.ResultsCorrelations between SES indicators were weak to moderate. Low academic performance (OR=1.96, 95% CI 1.53 to 2.51) and low SSS (OR=2.75, 95% CI 2.12 to 3.55) were the strongest indicators of poor SRH after adjusting for other SES-indicators. Results for SSS were consistent across countries, while associations with academic performance varied. Low academic performance (OR=5.71, 95% CI 4.63 to 7.06) and more pocket money (OR=0.21, 95% CI 0.18 to 0.26) were most strongly associated with smoking in all countries.ConclusionsSocioeconomic inequalities in adolescent health were largest according to SES indicators more closely related to the adolescent’s education as well as the adolescent’s perception of relative family SES, rather than objective indicators of parental education and material family affluence. For future studies on adolescent health inequalities, consideration of adolescent-related SES indicators was recommended.