1. Clawson HJ, Layne M, Smalls K. Estimating human trafficking into the United States: development of a methodology: final phase two report. Fairfax, VA: ICF International; 2006.
2. US Department of State. Trafficking in persons report. Washington, DC: US Department of State; 2015.
3. Nawyn SJ, Birdal NBK, Glogower N. Estimating the extent of sex trafficking: problems in definition and methodology. Int J Sociol. 2013;43(3):55–71.
4. Siskin A, Wyler LS. Trafficking in persons: US policy and issues for congress. Washington, DC: Congressional Research Service; 2012.
5. United Nations Office on Drugs and Crime (UNODC). Global report on trafficking in persons. Vienna: United Nations; 2014.