What causes human trafficking? This is not an easy question to answer. Increased globalization, neo-liberalism, economic inequalities, conflict, and corruption all are potential factors in motivating traffickers and making victims vulnerable to this kind of exploitation. Yet, as it is a hidden crime, how can we know more about the causes?
We have a tool to fight human trafficking, a tool that we are not using to its full potential. This tool is quantitative data.
Methodology is important when calculating the number of victims. The ‘dark figure’ is a term used to speak about unreported crimes, or in this case, the missing data from law enforcement systems. A good methodology for establishing high quality data must take into account this dark figure. Bales, Hesketh, and Silverman explain how multiple systems estimation and the mark-recapture method can be used to estimate the number of victims of modern slavery. These methods are effective in quantifying hidden crimes. The mark-recapture method is conducted by taking samples from a population, noting the number in each sample as well as the overlap between the two of them. Then probability theory is used to make an estimate of the total population in question. Multiple systems estimation uses this same method, but increases the number of samples so multiple lists are examined. It has been used to study other human rights violations that are difficult to quantify, such as civilian deaths in armed conflict.
Politics surrounding the definition of human trafficking also lead to confusion about numbers. Often governments, NGOs, academics, and lawyers can agree to reduce trafficking, but disagree on labor issues, migrants’ rights, or positions on prostitution. This disagreement can hinder progress. Governments are often unlikely to share numbers that reflect badly on them. Organizations might use sensationalized statistics and play on moral panic inducing images and phrases in an effort to raise awareness of an issue. Both the Walk Free Foundation and the International Labour Organization (ILO) publish numbers on modern slavery. The numbers differ because of different methodologies, but also a difference in definition of slavery. The Walk Free Foundation includes forced marriage in its definition of modern slavery, while the ILO does not.
We know that human trafficking is increasing. But we also know that we have the power to do something about it. Check out the Polaris Project, the Walk Free Movement, and Free the Slaves for ways you can get involved in the global fight against trafficking.
 Cameron, S. and Newman, E. eds. (2008) Trafficking in Humans. Tokyo: United Nations University Press.
 Andreas, P. and Greenhill, K. eds. (2010) Sex, Drugs, and Body Counts: The Politics of Numbers in Global Crime and Conflict. Ithaca: Cornell University Press.
 De Cock, M. (2013) There’ll Be No End to Forced Labor and Slavery Without Data. The Guardian. Available at: http://www.theguardian.com/global-development-professionals-network/2013/aug/29/slavery-forced-labour-data. [Accessed 20 June 2013].
 Tyldum, G. (2008) Coping with Biases in Human Trafficking. In Aghazarm, Christine, Frank Laczko, et al. eds. Human Trafficking: New Directions for Research. [online] International Organization for Migration. Available from: https://www.iom.int/ jahia/webdav/shared/shared/ mainsite/microsites/IDM/worksops/ensuring_protection_070909/human_trafficking_new_directions_for_research.pdf [Accessed 5 August 2015]. pp. 27-43.
 Bales, K., Hesketh, O., and Silverman, B. (2015) Modern Slavery in the UK: How many victims? Significance. 12(3) 16-21.
 Farrell, A. and McDevitt, J. (2008) Enhancing the Collection and Standardization of Human Trafficking Data: Examples for Data Collection Efforts in the United States. In Aghazarm, Christine, Frank Laczko, et al. eds. Human Trafficking: New Directions for Research. [online] International Organization for Migration. Available from: https://www.iom.int/jahia/webdav/shared/ shared/mainsite/microsites/IDM/worksops/ensuring_protection_070909/human_trafficking_new_directions_for_research.pdf [Accessed 5 August 2015]. pp. 15-26.