The analysis in this article was based on data from Thomas Piketty and collaborators, who have also compiled an extremely detailed and comprehensive analysis of the subject of capital & wealth & inequality. I highly recommend Piketty's book, "Capital in the 21st Century" (see Goodreads comments for abridged summaries and reviews by readers). Not only is it totally convincing (and depressing), but it also provides a very clear understanding of the course of modern history since the 19th century. It's amazing to see how clear economic policy (whether Marxist or Capitalist or anything in between) becomes when viewed through the lens of society grappling with the problem of capital/income/inequality.
https://www.goodreads.com/book/show/18736925-capital-in-the-...