Do domestic immigrants live longer? An approach for estimating the life expectancy of small populations

Ageing is a major demographic issue for the world of the 21st century and is caused by substantial declines in fertility and mortality rates. Without international migration, most developed countries would not be able to balance the resulting losses of population and work force. The proportion of elderly (aged 65 and over) in Taiwan reached the threshold of 7%, indicating an ageing society, in 1993, and has been increasing dramatically since then. The county-level populations in Taiwan are also ageing rapidly, but the local changes vary widely because domestic migration rates of each county are different. Urbanization is becoming more obvious, with people tending to move to large cities and counties with better social welfare programs. As a result, domestic migration plays an important role in population ageing at the county level, and the people in counties with larger numbers of domestic immigrants are expected to have a longer life expectancy. However, the life expectancies of people in these counties do not bear out this trend. In the present study, based on domestic migration records from the Department of the Interior of Taiwan, we applied graduation methods and small-area estimation skills to construct county-level life tables, and evaluate whether domestic immigrants have lower mortality rates than those who do not migrate. We found that the domestic immigrants of Kinmen County have significantly lower mortality rates, but those of Hsinchu County do not.