Slave traders today make a return on their investment 25 to 30 times higher than their 18th- and 19th-century counterparts.
Siddharth Kara, a slavery economist and fellow of the Carr Center for Human Rights Policy at the Harvard Kennedy School, has calculated that the average profit a victim generates for their exploiters is $3,978 (£3,030) a year. Sex trafficking is so disproportionately lucrative compared to other forms of slavery that the average profit for each victim is $36,000.
In his book Modern Slavery, to be published in October, Kara estimates that sex trafficking accounts for 50% of the total illegal profits of modern slavery, despite sex trafficking victims accounting for only 5% of modern slaves.
Kara based his calculations, shared exclusively with the Guardian, on data drawn from 51 countries over a 15-year period, and from detailed interviews with more than 5,000 individuals who have been victims of slavery.