The study on earning power also said American families' incomes had been far behind productivity since 2000, The Wall Street Journal reported.
"The up escalator that has historically ensured that each generation would do better than the last may not be working very well," said the study.
The study on economic mobility was prepared by several think tanks, including the Pew Charitable Trusts, the Brookings Institution, the Heritage Foundation, American Enterprise Institute and the Urban Institute.
The median income for a man in his 30s in 2004 was $35,010, 12 percent less than in 1974, his father's generation, when adjusted for inflation, the Journal reported.
Ten years ago, the median income for men in their 30s was 5 percent higher than it was 30 years earlier.
"It seems there's been some slowdown in economic growth, it's possible that the movement of women into the labor force has affected male earnings and it's possible that men are not working as hard as they used to," Isabel Sawhill of the Brookings Institution told the newspaper.
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