Newspaper headlines trumpeted that the middle class is shrinking, but to a large extent that is because people are moving into the upper middle class, not because they are getting poorer.
By one measure, the middle class has shrunk from 38% of the US population in 1980 to 32% today but at the same time the upper middle class has grown from 12% to 30% of the population today.
Josh Zumbrun at the WSJ has an excellent piece on new research from the (liberal-leaning) Urban Institute and elsewhere:
There is no standard definition of the upper middle class. Many researchers have defined the group as households or families with incomes in the top 20%, excluding the top 1% or 2%.
Mr. Rose, by contrast, uses a more dynamic method similar to how researchers calculate the poverty rate, which allows for growth or shrinkage over time, and adjusts for family size.
Using Census Bureau data available through 2014, he defines the upper middle class as any household earning $100,000 to $350,000 for a family of three: at least double the U.S. median household income and about five times the poverty level. At the same time, they are quite distinct from the richest households. Instead of inheritors of dynastic wealth or the chief executives of large companies, they are likely middle-managers or professionals in business, law or medicine with bachelors and especially advanced degrees.
Smaller households can earn somewhat less to be classified as upper middle-class; larger households need to earn somewhat more.
Mr. Rose adjusts these thresholds for inflation back to 1979 and finds the population earning this much money has never been so large. One could quibble with his exact thresholds or with the adjustment that he uses for inflation. But using different measures of inflation, or using higher income thresholds for the upper-middle class, produces the same result: substantial growth among this group since the 1970s.