A pedestrian walks along Lambeth Road in south London on Friday. Police have rescued three women from a home in the neighborhood. They were held hostage for some 30 years, according to authorities. Andy Rain/EPA/Landov hide caption

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Child laborers wait to be processed at a safe house after being rescued during a raid at a factory in New Delhi by workers from Bachpan Bachao Andolan (Save the Childhood Movement) in June. Kevin Frayer/AP hide caption

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Listen to All Things Considered's Audie Cornish interview study author Kevin Bales.

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Prostitutes arrested in Guatemala City in 2012, as part of an operation against human trafficking. Johan Ordonez/AFP/Getty Images hide caption

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