Joseph Stiglitz in his book Freefall, and Robert Reich in his Aftershock, have told similar stories, while the economists Michael Kumhof and Romain Ranciere have devised a formal mathematical version of the possible link between income concentration and financial crisis. While the underlying models differ, the Keynesian versions emphasize that if the super-rich save a lot, ever-increasing income concentration can be expected to lead to a chronic excess of planned savings over investment.