A copy of a 2010 Census form is shown at...

A copy of a 2010 Census form is shown at a Census Day event in Caldwell, Idaho. (April 1, 2010) Credit: AP

Nonfamily households showed double the growth of family households in the decade ending in 2010, which also saw increases in those of multiple generations living under one roof and of interracial couples, a new U.S. Census Bureau report says.

"We found households are becoming more diverse," Daphne Lofquist, a bureau statistician, told reporters in a teleconference Wednesday.

Between 2000 and 2010, the number of nonfamily households grew 16 percent -- rising from 33.6 million in 2000 to 39.2 million in 2010 -- while family households grew by 8 percent over the same period, the bureau's analysis of 2010 census data showed.

Nonfamily households include people who live alone or nonrelatives living together, such as unmarried partners or roommates.

Nestled in the numbers, area experts said, are important changes that speak not only to demographic shifts but cultural ones as well.

Lee Koppelman, director of Stony Brook University's Center for Regional Policy Studies, said several factors are at work in the growth of nonfamily households. The aging of the population is one. "You wind up with a single head of household simply because one partner has passed away," he said.

There's a cultural shift, too: It's now more socially acceptable for couples to live together without being married, Koppelman said. Economic factors also may play a role, driving young adults to move in together because they can't afford rent on their own, he said.

Family households still predominate nationally, making up 77.5 million out of 116.7 million households. But their share is declining, down to 66 percent of all households in 2010, from 68 percent in 2000.

Over the decade, the share of nonfamily households increased from 32 percent to 34 percent, the report said.

The 2010 census also marked a first. It is the first decennial census to show the share of husband-and-wife households dipping below 50 percent of all households -- to 48.4 percent, down from 51.7 percent in 2000 -- said Rose Kreider, chief of the bureau's Fertility and Family Statistics Branch. The bureau first asked the question on family relationships in 1940. "What we're seeing is a continuation of trends" noted in earlier studies, she added.

According to the report, unmarried-partner households increased about 40 percent between 2000 and 2010, growing from 4.9 million in 2000 to 6.8 million in 2010. Interracial and "inter-ethnic" marriages increased 28 percent over the decade, with the report finding high rates of couples made up of Hispanics and non-Hispanics.

Peter Salins, a political science professor at Stony Brook and director of its Graduate Public Policy Program, said the statistics raise societal concerns.

"The erosion of the family households is probably most associated with the aging of the American population," Salins said.

He added that "two phenomena that are the ones to notice" are the growth in single-parent households, the largest of which consist of women heading families, and the trend among young adults to delay marriage.

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