Selective migration, health and deprivation: a longitudinal analysis.

Population migration is a major determinant of an area's age-sex structure and socio-economic characteristics. The suggestion that migration can contribute to an increase or decrease in place-specific rates of illness is not new. However, differences in health status between small geographical locations that may be affected by the inter-relationships between health, area-based deprivation and migration are under-researched. Using the Office for National Statistics (ONS) England and Wales Longitudinal Study (LS) 1971-1991, this research tracks individuals to identify any systematic sorting of people that has contributed to the area-level relationships between health (limiting long-term illness and mortality) and deprivation (Carstairs quintiles). The results demonstrate that among the young, migrants are generally healthier than non-migrants. Migrants who move from more to less deprived locations are healthier than migrants who move from less to more deprived locations. Within less deprived areas migrants are healthier than non-migrants but within deprived areas migrants are less healthy than non-migrants. Over the 20 year period, the largest absolute flow is by relatively healthy migrants moving away from more deprived areas towards less deprived areas. The effect is to raise ill-health and mortality rates in the origins and lower them in the destinations. This is reinforced by a significant group of people in poor health who move from less to more deprived locations. In contrast, a small group of unhealthy people moved away from more deprived into less deprived areas. These countercurrents of less healthy people have a slight ameliorating effect on the health-deprivation relationship. Whilst health-deprivation relationships are more marked for migrants there are also health (dis-) benefits for non-migrants if their location becomes relatively more or less deprived over time. Overall we found that between 1971 and 1991, inequalities in health increased between the least and most deprived areas, compared with the health-deprivation relationship which would have existed if peoples' locations and deprivation patterns had stayed geographically constant. Migration, rather than changes in the deprivation of the area that non-migrants live in, accounts for the large majority of change.