https://www.kcl.ac.uk/policy-institute/assets/uk-attitudes-to-immigration-1018742pub01-115.pdf
http://blogs.lse.ac.uk/brexit/2018/05/15/switzerland-wanted-more-immigration-controls-but-economic-self-interest-will-probably-prevail/
https://www.tandfonline.com/doi/full/10.1080/13511610.2021.1968355
http://publications.iom.int/system/files/pdf/global_migration_indicators_2018.pdf