Area variations in health outcomes: artefact or ecology

It is a long-standing belief that the size of the difference between the poor (lower social groups) and the rich (higher social groups) in health outcomes will vary according to the characteristics of the area. However typical approaches to analyses of this kind of question violate standard statistical assumption. The basic problem is how to estimate the size of a 'ward effect' (the disadvantage of living in a 'poor' ward over and above effects associated with individual or household circumstances). This is complicated by the hypothesized existence of intra-ward correlated errors; the only way to avoid this bias is to explicitly model the different variance components using multi-level modelling techniques. The purpose of this paper is to illustrate this technique. Analysis using several of the health outcomes in the Health and Lifestyle Survey data, suggests that the ward effect is quite substantial, and remains after 'controlling for' age, gender and several other socio-demographic variables. This 'ward effect' appears to be best represented by the proportions without access to a car and the preponderance of working class members (RGSC IV and V) in the population. Whilst the verdict on the original hypothesis remains 'not proven', the hypothesis has been shown to be more complex than its simplistic statement suggests. The analyses have shown how to unpack these complexities and, more generally, have illustrated the power of the multi-level modelling technique.