About 45.8 million people around the world are trapped in modern versions of enslavement, a human rights group reported Tuesday, 28 percent more than its last estimate two years ago.

The organization, the Walk Free Foundation, attributed the increased number in its report, the 2016 Global Slavery Index, to improved data collection and research methodology. Whether enslavement is increasing or decreasing remains unclear.

The organization said it had derived the index from 42,000 interviews conducted in 53 languages. Some form of modern slavery exists in all 167 countries covered by the index, it said.

Unlike historical definitions of slavery in which people were held as legal property, a practice that has been universally outlawed, modern slavery is generally defined as human trafficking, forced labor, bondage from indebtedness, forced or servile marriage or commercial sexual exploitation.