CBS Local — While adulthood usually signals a certain amount of independence, a new study has found that more adults are living with roommates or parents than at any point in the last three decades.

Online real estate database Zillow says that 30 percent of adults between ages 23 and 65 were living in “doubled-up households” in 2017. The government defines a “doubled-up” home as two or more adults (not counting spouses or partners) who live in the same house. Zillow’s researchers say it’s the largest number of adults co-habitating since 1990. Much of the blame for the growing number of roommates was pointed at the rise in rent costs across the United States.

“As rents have outpaced incomes, living alone is no longer an option for many working-aged adults,” Zillow senior economist Aaron Terrazas said in a press release.

“By sharing a home with roommates — or in some cases, with adult parents — working adults are able to afford to live in more desirable neighborhoods without shouldering the full cost alone.”

Zillow’s study also found that adults who live with roommates were paid less; earning 67 cents for every dollar an adult living on their own was making in 2017.

Only 23 percent of adults were found to be doubling up in 1990 and 22 percent in 2000. While smaller cities have been less affected by the trend, the country’s biggest population centers have seen more and more people being forced to live together. In New York and Los Angeles, where the average rent exceeded $2,300 a month, more than 40 percent of adults were living with roommates this year.

New York and California were also found to be two of the least affordable states to live in, with nearly half of a person’s income going to the rent each month.