Home » Research » Improving the Statistics and Prevalence Data on Human Trafficking in the United States

Improving the Statistics and Prevalence Data on Human Trafficking in the United States


Lisa Fedina is a PhD student in the School of Social Work at the University of Maryland, Baltimore. Her research interests include family and gender-based violence, sex trafficking, trauma, and violence prevention. She has worked with adult and child sex trafficking victims and also managed a statewide anti-trafficking initiative led by the Illinois Department of Human Services in partnership with the U.S. Department of Health and Human Services. She is a member of the National Research Consortium on Commercial Sexual Exploitation.


Nearly 15 years have passed since human trafficking was first legally recognized and criminalized under the U.N. Protocol to Prevent, Suppress, and Punish Trafficking in Persons (2000) and the U.S. Trafficking Victims Protection Act (2000). To date, the U.S. federal government has allocated over 500 million dollars to combat human trafficking domestically and internationally; yet, only 2,515 domestic human trafficking incidents were investigated by law enforcement between the years of 2008 and 2010; and only 46,000 human trafficking victims were identified worldwide in 2012 (note: this is the most recent data available). Similarly, the U.S. Department of Justice prosecuted only 125 human trafficking cases in 2011, though this was a 19% increase from 2010 and the highest number of cases prosecuted in one year. Human trafficking has certainly received a great deal of attention over the past decade and the number of trafficking prosecutions seems to be improving, but our understanding of the overall scale of the problem and the number of victims in the U.S. and globally remains unknown. Attempts have been made to measure the problem, but these estimates are unreliable, based on flawed or unscientific methodologies, and are vastly disproportionate from one another.


In a recent systematic review, I surveyed a sample of books (n = 42) on sex trafficking published between the years of January 2005 and October 2012. The purpose of this review was to identify the most common sources of prevalence data being cited in books on sex trafficking and to explore the ways in which these data were being represented. This review was also conducted in response to recent academic and public discourse on pressing issues within current human trafficking research and, consequently, within the larger anti-trafficking movement. Ongoing debates on the true scope of the problem often lead to the conclusion that existing estimates on victims are likely inflated and anti-trafficking organizations are seemingly exaggerating the issue of human trafficking. Previous researchers have not only raised important questions about the validity of the current estimates, but have also pointed out significant discrepancies between these estimates and the actual number of victims identified in the U.S. and globally. McGaha and Evans refer to this problem as the “Credibility Gap” in human trafficking research and indicate that inflating the problem of human trafficking ultimately does more harm than good for anti-trafficking efforts.


There were three most commonly cited sources of prevalence data in the sample of books reviewed: 1) U.S. State Department, 2) Dr. Kevin Bales, and 3) Drs. Richard Estes and Neil Weiner.


1) The U.S. State Department has published four separate Trafficking in Persons (TIP) reports where estimates of the number of victims trafficked annually into the U.S. and worldwide are provided. The first estimate (2001) suggested that 700,000 victims were trafficked globally and 45,000-50,000 were trafficked into the U.S. each year. In 2003, the U.S. estimate was revised from 45,000-50,000 to 18,000-20,000 victims in the U.S. annually and revised again in 2004 to 14,500-17,500 victims. In 2007, the State Department revised its global estimate from 700,000 to 800,000. The methodologies behind these estimates have been previously evaluated for rigor and reliability. Specifically, the U.S. Government Accountability Office pointed out serious flaws in the methods used to derive each of the estimates. McGaha and Evans also provided insight into the reasons for the State Department’s revisions. Specifically, the multiple revisions are a reflection of methodology changes over the subsequent years; however, the statistics remain an “estimate of estimates” rather than an estimate based on actual known or reported cases. McGaha and Evans and Footen Bromfield and Capous-Desyllas also explore how these (flawed) estimates ultimately led to the formation and passage of the TVPA in 2001. A total of 64% of books reviewed cite the State Department estimates.


2) Dr. Kevin Bales has published three editions of his book Disposable People: New Slavery in the Global Economy (1999, 2004, 2012), where he estimates that 27 million people are enslaved at any given time throughout the world. Bales has published articles on human trafficking in at least two peer-reviewed journals (i.e. Scientific American in 2002 and Comparative Labor Law and Policy in 2004) where he discusses the problems of generating accurate numbers of victims and is transparent about the flaws of his own estimate (see the recent systematic review for further exploration of Bales’ statistic).Still, no scientific methodology seems to have been used to develop the statistic, other than consulting other anti-trafficking experts and using his own experience to inform the estimate. A total of 34% of books cite Bales’ data and at least one book (Not For Sale by David Batstone) uses Bales’ estimate to create a new projection of the number of victims worldwide (from 27 million to 30 million slaves worldwide).


3) Dr. Richard Estes and Dr. Neil Alan Weiner conducted a study in 2001 on the Commercial Sexual Exploitation of Children in the U.S., Mexico, and Canada. The first estimate concluded that 326,000 children were at-risk of commercial sexual exploitation in the U.S.; however, this estimate was reduced in 2002 to 244,000 children at-risk in the U.S. as a result of inconsistencies found in the methodology used to derive the original estimate. The Crimes Against Children Research Center (CACRC) examined the reliability of these estimates and identified major methodological flaws in both the original and revised versions. A total of 27% of books cite this estimate and several confuse the estimate as the actual known number of U.S. children trafficked into the sex industry as opposed to an estimate of the number of children at-risk of being exploited.


Overall, 79% of books relied on at least one of the three unreliable prevalence data sources. Educating the public and raising awareness on the issue of human trafficking has been a cornerstone of the larger anti-trafficking movement and agenda in the U.S. Since the public often seeks out mainstream sources of education, including books, using unreliable data in books misrepresents the issue and misinforms the public. Using flawed data can also lead to inappropriate allocations of funding for victim services, program evaluation, training and education, research, and criminal prosecutions. Additionally, McGaha and Evans explain how using “bad data” threatens the credibility and success of what anti-trafficking advocacy efforts have achieved thus far. There is a great need for researchers, practitioners, and advocates working on human trafficking to develop and disseminate consistent and accurate messaging on the problem. Until better prevalence data emerge, individuals and organizations addressing this issue should be transparent in communicating (to the public and to stakeholders) that reliable and accurate estimates of the problem do not currently exist.


At least two recent studies have offered new insight into the scope of the problem. First, researchers at Northeastern University and the Urban Institute, who concluded that deriving a single estimate was impossible, derived three estimates of trafficking victims in the U.S. based on known and reported counts of cases identified through a variety of open sources (e.g. through media reports, law enforcement data, and local prevalence studies). The first estimate, considered the most reliable of the three since it was based on actual counts of victims collected through national surveys, included 5,166 victims. The last two (22,209 and 60,467 trafficking victims) were estimates generated from multiplying counts of cases using local prevalence studies and economic modeling data techniques.


Second, the Urban Institute recently released a report in March 2014 on the Size and Structure of the Underground Commercial Sex Industry in eight major U.S. cities and employed a different approach by estimating revenue generated from the sex industry rather than estimating numbers of sex trafficking victims, as demonstrated in prior prevalence studies. Instead, this study used qualitative interviews with key informants and analyzed secondary data sources on illicit economies and risk behaviors (e.g. National Survey of Drug Use and Health and the National Youth Risk Behavior Survey) to derive estimates of the revenue generated by the underground commercial sex economy in each of the cities. Estimates ranged from $39.9 to $290 million among the eight cities. The study also assessed the overlap between other underground economies (i.e. weapons trafficking, drug trafficking, and gang involvement) and found increasing connections between gang involvement in sex trafficking and prostitution in five of the eight cities. Although they have substantially improved our understanding of the extent of human trafficking, these studies are certainly not without limitations and focus only on certain characteristics of the crime.


Indeed, human trafficking is a clandestine activity that is extremely difficult to measure. Still, reliable estimates are necessary in order to equip local and federal governments, accurately inform practice and policy efforts, and to provide clear objectives for future research on human trafficking. Ongoing, organized, and combined data collection efforts – as well as program evaluation – among anti-trafficking organizations, service providers, and law enforcement agencies can serve as robust data sources to generate more reliable estimates of the extent of human trafficking.


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