Global studies from Pew Research Center in 2014 and 2017 ranked the Chinese government's restrictions on religion as among the highest in the world, despite low to moderate rankings for religious-related social hostilities in the country. The Global Slavery Index estimated that in 2016 more than 3.8 million people were living in "conditions of modern slavery", or 0.25% of the population, including victims of human trafficking, forced labor, forced marriage, child labor, and state-imposed forced labor. The state-imposed forced system was formally abolished in 2013, but it is not clear to which extent its various practices have stopped. The Chinese penal system includes labor prison factories, detention centers, and re-education camps, which fall under the heading Laogai ("reform through labor"). The Laogai Research Foundation in the United States estimated that there were over a thousand slave labour prisons and camps, known collectively as the Laogai.