Material deprivation was measured using the ward-based socioeconomic status rankings derived from the maternal residential geocoded address. The ward-based socioeconomic status ranking was extracted from the Israeli Central Bureau of Statistics (based on the 1995 census data) and reflects various socio-economic measures characterizing the ward's population, including income, parents' education, apartment size, possession of appliances, and car ownership. The ranking represents, to a considerable extent, individual risk factors and possible confounders. It should be noted that the statistical wards are designed a priori to include relatively homo- generous populations with respect to ethnicity, lifestyle, social class, and deprivation (Central Bureau of Statistics, 2011). A higher ranking indicates a higher socioeconomic status. This is in turn, known to be negatively correlated with parental smoking and child exposure to environmental tobacco smoke (Muhsen, 2006). We included the ward-based socioeconomic status in the regression using three categories (low, medium and high status).