Does migration exaggerate the relationship between deprivation and limiting long-term illness? A Scottish analysis.

Few epidemiological studies of the links between health and environmental variables account for the potentially confounding effects of population migration. Here we explore the relationship between self-reported limiting long-term illness and material deprivation, using individual-level 1991 census data extracted for Scotland. The aim is to investigate whether the migration patterns of ill individuals influences the relationship between limiting long-term illness and material deprivation. Specifically, we seek to determine whether individuals who are well are more likely to migrate away from deprived areas and whether ill individuals are more likely to migrate towards deprived areas. If true, this would suggest that the apparent relationship between deprivation and limiting long-term illness is exaggerated by the effects of migration. We then examine the issue controlling for individual-level characteristics expected to influence limiting long-term illness and pay special attention to the role of public housing in these relationships.