http://ftp.iza.org/dp9466.pdf
https://euagenda.eu/upload/publications/untitled-111339-ea.pdf
https://papers.ssrn.com/sol3/Delivery.cfm/SSRN_ID3934683_code1082902.pdf?abstractid=3479439&mirid=1
http://wir2018.wid.world/files/download/wir2018-summary-german.pdf