Decomposition of passive smoking inequality in Iranian children and adolescents: the CASPIAN-V Study.

To investigate the socioeconomic inequality in passive smoking in Iranian children and adolescents. Through a multistage random cluster sampling method, a representative sample of 14,400 school students, aged 6-18 years, were enrolled from urban and rural areas of 30 provinces of Iran. Using a non-linear principal component analysis (NLPCA), the correlated variables were summarized as socioeconomic status (SES). Normalized concentration index (NCI) was used to measure inequality in passive smoking at national and regional SES levels. We decomposed total socioeconomic inequality in passive smoking into explanatory variables to identify the main contributors of inequality in passive smoking in the population studied. Data of 12,327 students and parents were complete for the current study. The response rate was 85.6% (50.9% boys, 71.2% urban residents). About 44% of Iranian students were exposed to passive smoking. The NCI for passive smoking at a national level was - 0.043 (95% confidence interval - 0.035, - 0.012), indicating that passive smoking was more concentrated among poorer children and adolescents. This inequality was statistically significant at a national level and in all regions except for regions with lower middle- and lowest SES levels. Considering the decomposition analysis, the household SES (63%), mothers' educational level (37%), fathers' educational level (29%), and school type (18%) made the largest positive contribution to inequality in passive smoking of children and adolescents. Passive smoking was distributed unequally among Iranian children and adolescents; it was more concentrated among socioeconomically disadvantaged families. Public health policies attentions should be given to reduce passive smoking among low SES children and adolescents living with illiterate or low-educated parents.