Mortality among migrants and their descendants living in England and Wales
In this article, Matthew Wallace analyses adult mortality (from age 20) among international immigrants in England and Wales and investigates possible explanations why immigrants have lower death rates than natives. Specifically, he investigates the hypothesis that this ‘migrant mortality advantage’ is generated by two types of bias inherent in the study of migrant populations: censoring bias (the under-registration of migrant departures) and salmon bias (the large-scale remigration of ill migrants).
The author first analyzes the impact of censoring bias. In England and Wales, it is not a legal obligation for immigrants to inform the authorities that they are leaving the country, so many fail to do so. Consequently, because we do not know when these migrants leave we become prone to over-estimating their length of stay and producing artificially low migrant death rates. To quantify the extent of this bias, Wallace uses information from census and administrative registers to generate a departure date for immigrants who can no longer be found in databases, but did not record an exit. He finds that censoring bias introduces some error, but cannot explain low migrant death rates.
The author then analyzes the impact of salmon bias. This theory is based on the principle that immigrants who return to their home country, especially at older ages, are less healthy and more likely to die than immigrants who remain in the host country. The deaths of these return migrants would not be counted in England and Wales’ vital statistics, producing artificially low death rates. The author found proof of the salmon bias among immigrants from India, Pakistan, Bangladesh, and Caribbean countries. Once again, though, this bias could not fully explain low migrant death rates.
After explicitly correcting the two types of bias and demonstrating that low immigrant mortality is real, Wallace studies immigrant mortality patterns in closer detail, finding that migrant death rates are lowest among young adults (immediately after they arrive in the host country) and increase with age (and length of stay). He also demonstrates that the migrant mortality advantage is driven by low cancer mortality, and in some groups, low cardiovascular disease mortality. Lastly, he shows that mortality among the descendants of immigrants is higher than immigrants’ and comparable to natives’. For specific groups, such as Black Caribbean, mortality among descendants is higher.
These findings corroborate selection theory, according to which individuals who migrate to another country do not constitute a random sample of the home country population but rather a sub-group with atypically robust health and low mortality. Cultural factors such as attitudes toward smoking and alcohol consumption must also play a role.
Further reading: 4 articles signed or cosigned by the author and accessible on line
2018, “Can the salmon bias effect explain the migrant mortality advantage in England and Wales?”, with Hill Kulu, Population, Space and Place, e2146.
2016, “Adult mortality among the descendants of immigrants in England and Wales: does a migrant mortality advantage persist beyond the first generation?” Journal of Ethnic & Migration Studies, 42(9): 1558-1577.
2015, “Mortality among Immigrants in England and Wales by Major Causes of Death 1971-2012: a Longitudinal Analysis of Register-Based Data”, with Hill Kulu, Social Science & Medicine, 147: 209-221.
2014, “Low immigrant mortality in England and Wales: a data artefact?” with Hill Kulu, Social Science & Medicine, 120: 100-109.
Source: Matthew Wallace, 2017, Mortality among migrants and their descendants living in England and Wales, Migration, health and survival : international perspectives / edited by Frank Trovato, Cheltenham, Northampton : Edward Elgar Publishing, chap. 10, p. 172-192.
Contact: Matthew Wallace
Online: December 2018