The American middle class is losing ground.

"After more than four decades of serving as the nation's economic majority, the American middle class is now matched in number by those in the economic tiers above and below it," writes the Pew Research Center in a report that analyzes the changing size, demographic, and economic status of the American middle class.

Pew Research defines middle class as "those with an income that is 67% to 200% (two-thirds to double) of the overall median household income, after incomes have been adjusted for household size. Lower-income households have incomes less than 67% of the median, and upper-income households have incomes that are more than double the median."

In addition to no longer being the majority, income growth for this segment of Americans is sluggish, the report finds. Since 1970, median income has risen for all classes of households, but the increase for upper-income households has outpaced the middle class increase by 13 percentage points. (And middle class median income outpaced that among lower-income households by another six percentage points.)

"The state of the American middle class is at the heart of the economic platforms of many presidential candidates ahead of the 2016 election," Pew Research writes. "Policymakers are engaged in debates about the need to raise the floor on wages and on how best to curb rising income inequality."

Read on to see the changing face of the middle class in nine revealing charts: