Figures for Iceland were actually extrapolated from figures for Britain. In all the index is pretty seriously flawed. Some countries are being ranked in the complete absence of any slavery data to justify a ranking.
It's mindblowing that something so statistically illiterate gets published. There is no way they can have the data to distinguish 23 from 0 (or 50) to any degree of confidence without actually enumerating the victims.
http://www.economist.com/news/international/21631039-interna...