The first of these factors, the prevalence estimates, were derived using a statistical process known as extrapolation. In 2015, Joudo Larsen, Bales and Datta published an article that describes the extrapolation process, and provides a test of it. Writing in Significance, the magazine of the UK Royal Statistics Society, Joudo Larson et al. note that the estimates in the 2014 Global Slavery Index involved several steps: