A recent Pew study has found that while middle class individuals remain the majority of the U.S. population, that proportion has shrunk by about 9 percent since the 1970s.

Pew said that in 1971 the country was composed of about 25 percent lower class individuals, 61 percent middle class, and 14 percent upper class. By contrast, in 2016, the country's population was 29 percent lower class, 52 percent middle class, and 19 percent upper class. 

Pew defined “Middle-income” Americans as adults whose annual household income is two-thirds to double the national median, after incomes have been adjusted for household size. In 2016, the national middle-income range was about $26,093 for single persons, $36,902 for couples, $45,195 for a family of three, $52,187 for a family of four, and $58,347 for a family of five. 

"Upper-income" is at least $78,281 for a single person, $110,706 for couples, $135,586 for families of three, $156,561 for a family of four, and $175,041 for a family of five. 

(Understanding that there are great variations in the cost of living from region to region, Pew has also included a calculator that takes location into account.)

Middle class households made slight gains between 2010 and 2016, with median income growing from $74,015 in 2010 to $78,442 in 2016, or roughly 6 percent. Upper-income households saw a median income gain from $172,152 to $187,872, or 9 percent. Lower-income households gained about 5 percent, $24,448 to $25,624. 

However Pew noted that middle class income is pretty much the same as it was in 2000, $78,056. It said that this is a reflection of lingering effects from recessions in 2001 and 2008. 

The most middle-income city in the U.S., with 65 percent of its population being middle class, was Sheboygan, WI. The most upper-income area was the San Jose-Sunnyvale-Santa Clara, Calif., region at 32 percent. The most lower income area was Laredo, Texas, at 49 percent.