Excerpt: In 2011, the middle-income tier included 51% of all adults, down from 61% in 1971. This has been accompanied by a dispersion of the population into the economic tiers both above and below, with slightly more moving into the upper tier. But only the upper tier has increased its share of the nation's total household income.
% of U.S. Total Household Income, 1970
% of U.S. Household Income, 2011
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