http://www.resolutionfoundation.org/app/uploads/2018/02/IC-international.pdf
https://www.socialeurope.eu/2017/07/49234/
http://ec.europa.eu/eurostat/statistics-explained/index.php/Acquisition_of_citizenship_statistics
https://eeas.europa.eu/sites/eeas/files/2_en_act_part1_v9_3.pdf?utm_source=POLITICO.EU&utm_campaign=ab6d830a9d-EMAIL_CAMPAIGN_2017_05_19&utm_medium=email&utm_term=0_10959edeb5-ab6d830a9d-189647205