<i>Is that raw numbers or as a percentage of the population?</i><p>He never answers this question. In terms of raw numbers, if the percentage stayed constant, you would expect to see a higher total number of slaves because the world population is constantly growing.<p>He also uses a much looser definition of slavery, including those who work for "no pay beyond subsistence". People falling into this category surely existed throughout history, along with the more obvious shackled slaves.
I think anyone focusing on whether there's actually more today than at any time in history is missing the point. This is not a contest. It's 27 million people's lives.