The percentage of families earning middle-class incomes fell in nearly nine out of 10 major metro areas across the country between 2000 and 2014, according to new research by the Pew Research Center. The study defined middle-class households as those making between two-thirds and twice the national median income. That was roughly $42,000 to $125,000 a year for a family of three in 2014, though adjustments were also made for the cost of living in different areas.