Raj Chetty, a professor of economics at Harvard and one of the authors, said in an interview that he and his colleagues still believed that a lack of mobility was a significant problem in the United States. Despite less discrimination of various kinds and a larger safety net than in previous decades, the odds of escaping the station of one’s birth are no higher today than they were decades ago.

The results suggested that other forces — including sharply rising incomes at the top of the ladder, which allows well-off families to invest far more in their children — were holding back talented people, the authors said.

“The level of opportunity is alarming, even though it’s stable over time,” said Emmanuel Saez, another author and a professor at the University of California, Berkeley. Mr. Saez and Mr. Chetty are both recent winners of an award for the top academic economist under the age of 40.