Socioeconomic differences in second-hand smoke exposure among children in Scotland after introduction of the smoke-free legislation

Background To examine the impact of the Scottish smoke-free legislation on social inequalities in secondhand smoke (SHS) exposure among primary school children.Methods Comparison of nationally representative, cross-sectional, class-based surveys carried out in the same schools before and after legislation. Participants were 2532 primary school children ( primary 7; aged around 11 y) surveyed in January 2006 ( before legislation) and 2389 in January 2007 ( after legislation). Outcome measures were salivary cotinine concentrations, self-reported family socioeconomic classification ( family SEC) and family affluence scale (FAS).Results After adjusting for number of smoking parents, mean cotinine concentration varied significantly across both family SEC and FAS groups, and increased significantly stepwise from high to low family SEC/FAS. Mean cotinine fell in all family SEC/FAS groups after legislation. The relative drop in mean cotinine was equal across all family SEC/FAS groups. Adding an interaction term between survey-year and family SEC/FAS to the model showed an increase in inequalities over time, but was only significant at the 93% level using FAS and 73% using family SEC.Conclusion Inequalities in SHS exposure exist among 11-year-old children in Scotland. Smoke-free legislation has reduced exposure to SHS among all children. Although the greatest absolute reduction in cotinine is observed in the lowest SEC/FAS group, cotinine levels remain highest for this group and there is a suggestion of possible increases in inequalities, which may warrant longer-term monitoring.