The "middle class" is an amorphous concept, and the presidential candidates are giving it their own definitions to fit their political purposes. Here are some ways to define it, political, economic and otherwise:
POLITICS: In pushing for tax benefits for "middle class" Americans, President Barack Obama defines them as families making less than $250,000 — which is 98 percent of U.S. households. He has also described them as having aspirations of owning a home, having affordable health care and being able to pay for their children's college educations. Republican challenger Mitt Romney has defined middle class as families making less than $200,000. He casts them as hard-working Americans who have been "kicked in the gut" in the weak economy.
WHITE HOUSE COUNCIL OF ECONOMIC ADVISERS: In a January speech noting the middle class has shrunk to 42 percent of households, Alan Krueger, who chairs the council, defined them as making annual earnings within 50 percent of the U.S. median income. The current median income is $49,445, putting middle-class earnings in a range from about $25,000 to $75,000.
ECONOMISTS: The Census Bureau divides household income into quintiles, or groups of 20 percent. Some economists narrowly define the middle class as those in the middle 20 percent of the distribution, earning between $38,000 and $61,000. Others define it more broadly to include the middle 60 percent, between $20,000 and $100,000. (The government's poverty line is based on the minimum income needed to have a basic standard of living, currently $22,314 for a family of four.)
SOCIOLOGISTS: The middle class to them is based on occupation: an "upper middle class" of white-collar specialists (lawyers, engineers, professors, economists and architects); and a "middle class" of lower-level white-collar workers (teachers, nurses, insurance sales and real estate agents). Together, they make up about 45 percent of households and sit near the upper end of the income distribution, just behind the top 1 percent.
POLLS: Americans often view "middle class" as something more than specific income levels, which can be affected by family size, expenses and local costs of living. At least two-thirds of adults say being middle class means owning a home, being able to save for the future and afford things like vacation travel, the occasional new car and various other little luxuries, according to an ABC News poll in 2010.
As a whole, roughly 95 percent of adults say they are middle class (50 percent), upper middle class (13 percent) or working class (32 percent), according to a separate Washington Post-ABC News poll in May. Just 2 percent described themselves as "better off" than upper middle class.