Does health-selective migration following diagnosis strengthen the relationship between Type 2 diabetes and deprivation?

Geographical health inequalities have been demonstrated for Type 2 diabetes in many developed countries, with poorer areas tending to have higher rates than wealthier areas. Previous studies have considered diabetes prevalence, relying on cross-sectional data collected from registers or hospital admissions records. However, the environment that had most influence on the development of a person's diabetes may not have been the same environment in which they are identified in a prevalence study. We therefore investigate whether health selective migration confounds the relationship between diabetes and deprivation by following a cohort of Type 2 diabetics from diagnosis until the end of the study, 8-18 years later. Our results demonstrate, first, that there is a significant relationship between material deprivation and diabetes incidence. Secondly, Type 2 diabetics in Tayside, Scotland have become more concentrated in relatively more deprived areas over time, strengthening the relationship between diabetes and material deprivation. Thirdly, and perhaps unexpectedly, this strengthening effect results primarily from selective immobility, rather than selective migration. We conclude that care should be taken when evaluating the relationship between diabetes and deprivation in cross-sectional studies. (C) 2007 Elsevier Ltd. All rights reserved.