https://www.eurofound.europa.eu/sites/default/files/ef_publication/field_ef_document/ef1663en.pdf
https://www.eurofound.europa.eu/sites/default/files/ef_publication/field_ef_document/ef1747en.pdf
https://www.eurofound.europa.eu/sites/default/files/wpef17037.pdf
https://www.ilo.org/wcmsp5/groups/public/—dgreports/—cabinet/documents/publication/wcms_662442.pdf