“Some of what’s happening is probably economics, because the great recession really hit young adults hard,” Dr. Fry said. “But I’m still struggling with the economic explanation, since the labor market for young adults has improved in the last five years, and yet the percentage living with their family is still going up. It seems to be somewhat decoupled from economics.”

Carlotta Mohamed, a 24-year-old student at the City University of New York’s Graduate School of Journalism who lives with her parents, said that because several of her friends, male and female, also lived at home, she did not think her situation was that unusual. But she does look forward to living independently soon.

“It would be nice to have my own space, but my parents are very supportive,” Ms. Mohamed said, adding that she had $40,000 of student debt. “I don’t pay any rent, but I do help out with cooking and cleaning. I hope I’ll be out of there when I’m 27 or 28. My mom stays awake until I come home.”

Rachel Franchi-Pereira, 21, a senior at Fordham, said she liked living at home, seeing it as an in-between phase, allowing her to remain in her comfort zone until she had a job and was ready to strike out on her own. “In my head, I see myself as an adult,” she said, “but I don’t know what kind of job I really want, I don’t know how to get an apartment, I don’t have to buy the toilet paper, and that’s what being adult is,” she said.

Through the 1940s and 1950s, the share of both sexes staying at home dropped, and by 1960, only about 20 percent of women and 30 percent of men were living with their parents or other relatives. The numbers have been rising since then, with a sharper uptick since 2000.