https://www.tandfonline.com/doi/full/10.1080/13511610.2021.1968355
https://read.oecd-ilibrary.org/social-issues-migration-health/international-migration-outlook-2018_migr_outlook-2018-en#page1
https://docs.iza.org/dp16728.pdf
http://ec.europa.eu/eurostat/statistics-explained/index.php/Acquisition_of_citizenship_statistics