How Can We Estimate Modern Slavery Globally?

The estimation of prevalence has been an important part of the process of bringing the crime of modern slavery and human trafficking to wide public and policy attention. The only large-scale estimate of modern slavery, presented with considerable background detail, is provided by the Global Estimates of Modern Slavery (GEMS), produced by two United Nations agencies together with Walk Free, an international charitable human rights group. Measuring the scale of modern slavery is a tough and complicated task. Modern slavery abuses are often hidden, or they may occur in countries where collecting data is difficult due to political instability. Given the challenges in estimating the prevalence of modern slavery, this article discussed some aspects of the estimation process, and reflect on issues it raises more generally for statistical analysis in difficult and important areas.