Invisible Emigrants: A Research Note Uncovering Population Over-Coverage Bias in Socio-Demographic Rates

This research note examines the impact of population over-coverage on socio-demographic indicators among migrants in Sweden. Over-coverage occurs when emigrants or deceased individuals remain in population registers, resulting in an overestimation of the resident population. This issue is particularly relevant for migrants due to increasing return, onward, and circular migration patterns. As register-based systems for population data collection become more prevalent, addressing over-coverage bias is critical. Using a Multiple Systems Estimation (MSE) method, this study adjusts for over-coverage in the Swedish population register and calculates accurate demographic and socio-economic rates. Administrative register data from 2003 to 2016 were analyzed to compute age-specific fertility rates, mortality rates, employment and unemployment rates, Total Fertility Rate, and Life Expectancy, focusing on foreign-born individuals. The results demonstrate that over-coverage substantially affects demographic and economic indicators, particularly at typical migration ages, with mortality rates exhibiting the largest bias at older ages. Consistent alignment of numerators and denominators, based on individuals' age and year of occurrence, ensured a robust analysis. These findings highlight the importance of addressing over-coverage to improve the reliability of socio-demographic insights in register-based population systems.