https://www.ipg-journal.de/regionen/global/artikel/detail/vorbei-mit-der-freiwilligkeit-4508/
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/662744/State_of_the_Nation_2017_-_Social_Mobility_in_Great_Britain.pdf
http://ec.europa.eu/social/main.jsp?catId=1143&intPageId=3193&langId=en/
https://www.etui.org/sites/default/files/2022-01/22%20Social%20policy%20in%20the%20European%20Union.%20State%20of%20play%202021.%20Social%20ambitions%20EU%20pandemic_2022.pdf