The Global Slavery Index is a yearly ranking of slavery conditions worldwide. It is published by the Walk Free Foundation and gives the index for each country. The first such index was out in 2013. It comprised of information about the vulnerability, prevalence and the nation-level responses. In 2013, the index was measured on a combination of three factors namely, the assessed incidence of slavery by population (this was done from primary as well as secondary sources of data), child marriage and human trafficking to and from of a country.