Table 2 Variability in intercept, 95 % confidence intervals (CIs) and Schwarz’s Bayesian Information Criterion (BIC) for a random intercepts model controlling for age (Model 1), a random intercepts model controlling for age and household position while adjusting for individual socio–economic position (Model 2), and a random intercepts model adjusting for individual socio-economic position and aggregate socio-economic characteristics of the sub-district (Model 3) (Belgium, 2001–2011)