Real Life Situation - Geography

In Mr. Pendergast's Geography class, you are beginning to examine the effect of disparities in the world. One of the resources he uses is a the following Tedtalk. In his Tedtalk, "How inequality harm societies," Richard Wilkinson concludes, "I think the take-home message though is that we can improve the real quality of human life by reducing the differences in incomes between us." What methods does Wilkinson use to justify this knowledge claim?
Here is an example of some TOK thinking on his talk. The knowledge questions recorded would be suitable for an entry in your TOK Field book.