Long-distance Migration and Mortality in Sweden: Testing the Salmon Bias and Healthy Migrant Hypotheses

Mortality research highlights the surprisingly low mortality of migrants to Europe and the US, despite their imminent disadvantages. Three main mechanisms may contribute to these patterns: 1) the so called “salmon effects” in mortality, being produced by situations when migrants opt to return to their country of origin in anticipation of death, 2) selective immigration of healthy migrants, and 3) the under-reporting of emigration. In our study, we test these hypotheses by focusing on the migration effects that may occur within a single country. We apply hazard regression to Swedish population registers to examine the age, duration-specific and time-varying influences of migration status on individual mortality during 1971-2007. The study covers 11.9 million Swedish born. About 473,000 people were born in Norrland and had moved, about 131,000 of them had returned. To distinguish between healthy-migrant and salmon effects we ask whether migrants from Norrland to Southern Sweden have lower mortality than the general population of Norrland and lower mortality than the population of Southern Sweden, whether return migrants to Norrland have a higher mortality than those who stay in the South, and whether patterns are altered by age. First results confirm that both mechanisms can be observed for the internal migrants in Sweden.