Neighbourhood influences on health

Abstract
Although multilevel studies help to tease apart contextual from compositional influences on health, they do not in themselves consider other threats to causal inference, particularly selection and endogeneity.1 Endogeneity occurs when people choose to move to a particular neighbourhood—for example, one with cleaner air or medical amenities—because of an existing health problem (reverse causation). Endogeneity can also occur because of the presence of unobserved common prior causes of neighbourhood-level exposures and health outcomes (confounding)—for example, it is commonly supposed that the presence of fast-food outlets in a neighbourhood increases the risk of obesity for local residents. However, it is equally plausible that the decision of fast food franchises to open their businesses in particular locations occurs in response to the tastes of local residents. In this instance, taste for fatty food is an unobserved variable that is related to both the location of outlets as well as the risk of obesity. Generally speaking, epidemiological studies to date have seldom attempted to deal with these threats to causal inference.