(Bloomberg) -- In the age of rising income inequality, the taskof preserving America’s middle class has been taken on bypoliticians across the ideological spectrum. A new report fromPew Research Center shows just how much theeconomic fortunes of this group have changed since the1970s.

In every decade since then, the percentage of adults living inmiddle-income households has fallen, according to Pew, which isbased in Washington. The share now stands at 50%, compared with 61%in 1971.

This matters because the "state of the American middleclass is at the heart of the economic platforms of manypresidential candidates ahead of the 2016 election," Pewresearchers Rakesh Kochhar and Richard Fry wrote in their report.Meanwhile "a flurry of new research points to the potential ofa larger middle class to provide the economic boost sought by manyadvanced economies."

Pew defines a middle-class household as one having income thatis two-thirds to double that of the overall median householdincome. A family of three, for instance, would need to have aminimum income of $41,869 to qualify as middle-income.

How America’s middle class has morphed

Being a member of the middle-class has long been treated as anAmerican badge of honor. However, middle-income households havelost their majority status in the U.S, with the size of theircounterparts on opposite ends of the income spectrum overtakingthem in number.

Some 120.8 million adult Americans lived in middle-classhouseholds this year, according to Pew. That’s slightly less thanthe combined number of upper-income adults (51 million) and thoseat the lower tier (70.3 million).

Their income gains are smaller

While households across the spectrum have seen higher earningsover the past several decades, upper-income households have seentheir pay rise the most.

The median income of those families was $174,625 in 2014, up 47%since 1970, Pew data show. That compares with a 34% gain for themiddle class and a 28% increase for the poorest households.

Households of all income levels got hit hard during therecession, resulting in earnings declines between 2000 and2014.

Blacks are least likely to be middle-income

Blacks are less likely to be part of the middle class than anyother racial or ethnic group, the Pew report finds. Some 45% ofblack adults were in the middle-income tier, down 1 percentagepoint from 1971.

One positive note is that blacks are the only major racial groupto see a decline over that time frame in their share of adults whoare low-income, which is down to 43% from 48%. Still, thatpercentage is the highest of the ethnic groups, alongsideHispanics.

White Americans are the only racial group where a majorityis in the middle class, though their share fell to 52% thisyear from 63% in 1971.

Their piece of the pie is shrinking

The middle class holds 43% of U.S. aggregate income, thesmallest share in Pew’s data back to 1970.

Almost half of aggregate earnings in the U.S. is now commandedby the wealthiest families, who are "are on the verge of holdingmore in total income than all other households combined," Kochharand Fry wrote. "This shift is partly because upper-incomehouseholds constitute a rising share of the population and partlybecause their incomes are increasing more rapidly than those ofother tiers."

Are you in the American middle class? Find out with Pew's income calculator.

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