By Mark Tutton, CNN
London (CNN)More than 40 million people were estimated to be victims of modern slavery in 2016 — and one in four of those were children.
Those are the findings of a new report produced by the International Labor Organization (ILO), a U.N. agency focusing on labor rights, and the Walk Free Foundation, an international NGO working to end modern slavery.
The report estimates that last year, 25 million people were in forced labor — made to work under threat or coercion — and 15 million people were in forced marriage.
It’s impossible to know exactly how many people are living in modern slavery, and different studies have produced different estimates. One reason is that modern slavery is a hidden crime that’s difficult to identify. Another is that different studies use different definitions of slavery, with some including forced marriage, for example, and others not.