https://www.opendemocracy.net/en/beyond-trafficking-and-slavery/exploitation-rule-not-exception/
http://www.cesifo-group.de/ifoHome/publications/working-papers/CESifoWP/CESifoWPdetails?wp_num=6452&CESifoWP.search=+
https://www.publications.parliament.uk/pa/cm201617/cmselect/cmwomeq/799/799.pdf