"2014 seems to have provoked unusual slavery stocktaking. The GSI 2013 was preceded by a survey in March 2013 by the SumAll Foundation, an American firm that deals in Big Data analysis. SumAll announced its arrival at a global slavery figure of 27 million, but its indifference of rigour vis-a-vis the GSI became evident later that year. Interestingly, SumAll had dredged up vassalage stats circa 1860: 25 million, estimated by the History Database of the Global Environment (2006). In effect, slavery has increased by 4.8 million in about a century-and-a-half."