Global Slavery Index

[5] The 2018 Global Slavery Index includes data on three key variables: the prevalence in each country, vulnerability and government responses.

Measurements of forced sexual exploitation, and of enslaved children, were identified as critical data gaps to address in future estimations.

Researchers Andrew Guth, Robyn Anderson, Kasey Kinnard and Hang Tran claimed that the 2014 Global Slavery Index's methods reveal weaknesses and raised questions about its replicability and validity.

For example, prevalence rates for Britain were applied to Ireland and Iceland, and those for America to western European nations, including Germany.

Gallagher writes that "the basic unit of measurement of 'modern slavery' is flawed: the definition is self-created and, bizarrely, changes from one year to the next".