Healthy or unhealthy migrants? Identifying internal migration effects on mortality in Africa using health and demographic surveillance systems of the INDEPTH network

Abstract

Migration has been hypothesised to be selective on health but this healthy migrant hypothesis has generally been tested at destinations, and for only one type of flow, from deprived to better-off areas. The circulatory nature of migration is rarely accounted for. This study examines the relationship between different types of internal migration and adult mortality in Health and Demographic Surveillance System (HDSS) populations in West, East, and Southern Africa, and asks how the processes of selection, adaptation and propagation explain the migration-mortality relationship experienced in these contexts. The paper uses longitudinal data representing approximately 900 000 adults living in nine sub-Saharan African HDSS sites of the INDEPTH Network. Event History Analysis techniques are employed to examine the relationship between all-cause mortality and migration status, over periods ranging from 3 to 14 years for a total of nearly 4.5 million person-years. The study confirms the importance of migration in explaining variation in mortality, and the diversity of the migration-mortality relationship over a range of rural and urban local areas in the three African regions. The results confirm that the pattern of migration-mortality relationship is not exclusively explained by selection but also by propagation and adaptation. Consequences for public health policy are drawn.

Cohort profile: internal migration in sub-Saharan Africa—The Migration and Health in Malawi (MHM) study

“…It has been challenging to empirically establish that migration causes changes in health due to the need to address (1) possible selection bias, that healthier (or in some cases, less healthy) individuals are more likely to migrate; 8–14 (2) the ‘salmon bias’ hypothesis, that less healthy individuals are more likely to return to areas of origin, and thus remaining migrants are relatively healthy; 9 12 14–19 and (3) the possibility that the effect of migration on health status changes over time: some research shows that the better health of migrants declines as they spend more time in their postmigration residence. 14 20–23 …”

Association between internal migration and epidemic dynamics: an analysis of cause-specific mortality in Kenya and South Africa using health and demographic surveillance data

“…Duration of residence in a new location has been found to reduce these effects as migrants adapt to their new environment. The hypothesis of adaptation suggests that over time, migrants’ health and behaviours may assimilate to non-migrants in a destination area, resulting in no discernible difference in health status between migrants and non-migrants [ 10 , 16 , 21 ].…”

Returning home to die or leaving home to seek health care? Location of death of urban and rural residents in Burkina Faso and Senegal

“…In the context of SSA, data collected in censuses and standard household-based surveys such as the Demographic and Health Surveys (DHS) do not allow a detailed analysis of rural–urban migration in relation to adult health [27,28]. First, these surveys do not collect often information on migration flows between urban and rural areas.…”