Human Trafficking Policy and Research Analysis Project: Comprehensive Review of Prior Prevalence Studies and Recommendations for Field Testing in the United States

Publication Date: July 7, 2021
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  • Published: 2021

Introduction

Research Questions

  1. What prevalence estimation strategies have been used successfully in prior human trafficking prevalence studies?
  2. What are the strengths and weaknesses of the main prevalence sampling methods for estimating trafficking?
  3. Which methods are most appropriate for estimating the prevalence of human trafficking in different industries?

Human trafficking negatively affects individuals, families, public safety, the healthcare system, and the criminal legal system. A critical step towards mobilizing effective anti-trafficking efforts involves estimating the scope of the problem. As part of the Administration for Children and Families’ Human Trafficking Policy and Research Analyses Project (HTPRAP), the RTI International research team is undertaking a focused prevalence inquiry of human trafficking in the U.S. The overarching goal of this task is to advance knowledge of promising methods for estimating human trafficking prevalence in the U.S. by field testing at least two methods of prevalence estimation within one industry and one geographic location in the United States.

As an initial step, the team: (1) conducted a comprehensive review of prior human trafficking prevalence studies focusing primarily on the sampling and estimation strategies that have been successfully used in prior research; (2) assessed the strengths and weaknesses of the main prevalence sampling methods for estimating trafficking; (3) considered how well each method could be used in different industries; and (4) developed recommendations for field testing prevalence estimation strategies in the United States. This report summarizes the findings and recommendation to date.

Purpose

This report summarizes the methods used in prior human trafficking prevalence estimation studies. This includes a discussion of the strengths and weaknesses of each method in general and as applied to specific industries. This report concludes with a recommendation for field testing two prevalence estimation studies within one industry and one geographic location in the United States.

Key Findings and Highlights

  • Prior prevalence studies have used a range of sampling and estimation strategies, including traditional probability samples (e.g., multistage, stratified, cluster), variants of multiple systems estimation and capture-recapture techniques, respondent-driven sampling and related link-tracing strategies, and other novel approaches.
  • Traditional probability samples used to estimate the prevalence of human trafficking have included both household- and school-based surveys. Although developing new large-scale surveys or adding questions to existing surveys would be powerful data collection mechanisms, doing so would not be efficient or feasible to meet the objectives of the current project. Probability samples developed for a specific industry in a limited geographic area allow for a more rigorous design than large-scale studies.
  • The use of multiple systems estimation or capture-recapture techniques to estimate human trafficking prevalence only makes sense when there is adequate existing data (e.g. administrative data or records) from which to sample. For most industries, there are no known existing data sources from which to sample.
  • Respondent-driven sampling and link-tracing are appropriate methods for developing samples of specific populations in smaller geographic areas and could be applied to many industries.
  • We recommend that HTPRAP’s targeted prevalence study use traditional probability sampling and link-tracing sampling methodologies to estimate the prevalence of labor trafficking victimization in the construction industry

Methods

Data from this report were gathered through a comprehensive literature review on prior research estimating the extent of human trafficking in various populations. A broad set of keywords were searched in numerous academic databases. Additional articles were then identified through reference lists of those picked up in the initial search.

Recommendations

After a systematic and comprehensive review of prior human trafficking prevalence studies and consideration of the feasibility of sampling within the priority areas listed above, we recommend that our targeted prevalence study utilize traditional probability sampling and link-tracing sampling methodologies to estimate the prevalence of labor trafficking victimization in the construction industry. We further recommend the addition of network scale up method (NSUM) as a no-cost, tag-along third estimation method that can be added to one of the survey techniques listed above.

Citation

Barrick, K. & Pfeffer, R. (2021). Human Trafficking Policy and Research Analyses Project: Comprehensive Review of Prior Prevalence Studies and Recommendations for Field Testing in the United States. OPRE Report No. 2021-XXX. Washington, DC: Office of Planning, Research, and Evaluation, Administration for Children and Families, U.S. Department of Health and Human Services.

Glossary

ACF:
Administration for Children and Families
OPRE:
Office of Planning, Research, and Evaluation
HTPRAP:
Human Trafficking Policy and Research Analyses Project
Sex trafficking:
As defined by the Trafficking Victims Protection Act, sex trafficking is a commercial sex act induced by force, fraud, or coercion, or in which the person induced to perform such an act has not attained 18 years of age.
Labor trafficking:
As defined by the Trafficking Victims Protection Act, labor trafficking consists of the recruitment, harboring, transportation, provision, or obtaining of a person for labor or services through the use of force, fraud, or coercion for the purpose of subjection to involuntary servitude, peonage, debt bondage, or slavery.