In 2010, the top 20 percent of Americans earned 49.4 percent of the nation's income, compared with the 3.4 percent earned by the some 15 percent of the population living below the poverty line, U.S. Census figures said.
Psychologist Shigehiro Oishi and Selin Kesebir, both of the University of Virginia, and Ed Diener of the University of Illinois said in the last 40 years, "we've seen that people seem to be happier when there is more equality."
"Income disparity has grown a lot in the U.S., especially since the 1980s," Oishi said in a statement. "With that, we've seen a marked drop in life satisfaction and happiness," in those 60 percent of U.S. adults with lower and moderate incomes.
The researchers analyzed General Social Survey from 1972 to 2008, which polled 1,500 to 2,000 random U.S. adults every other year -- resulting in a study sample of more than 48,000 respondents in 37 years.
The study, published in the journal Psychological Science, found although pocketbooks were thinner, the gap between people's own fortunes and those better off is correlated with feelings that other people are less fair and less trustworthy and this results in a diminished sense of well-being in general.
However, this inequality blues did not afflict those with top incomes -- income disparity or its absence did not affect the feelings about fairness and trust -- or their happiness -- of the richest 20 percent, the study said.