The income disparity between the wealthy and everyone else is at levels not seen since the Great Depression. Yet until now, economists haven't known what professions were driving this disparity. "Now a mounting body of economic research indicates that the rise in pay for company executives is a critical feature in the widening income gap," the Washington Post reported. A review of tax returns indicates that CEOs and other managers make up the largest percentage of the highest-income earners. And their pay has been skyrocketing. "Executive compensation at the nation's largest firms has roughly quadrupled in real terms since the 1970s, even as pay for 90 percent of America has stalled," the newspaper reported.