(Bloomberg Business) - - After shacking up with familyor friends for the last few years, millennials finally seem to bestriking out on their own.

The number of households grew by 1.48 million in the firstquarter from a year earlier, following a 1.66 million increase inthe final three months of 2014, according to data released Tuesdayby the U.S. Census Bureau. While the numbers can be volatile,it still marks the fastest back-to-back gains in householdformation since the second half of 2005.

The Census data don't break out age groups, so they don'tspecify who is forming these new households. But separate reportsshow the previous weakness in household formation was being drivenby millennials, or young adults born after 1980, so that groupis most likely driving the improvement as well, said Maury Harris,economist at UBS Group AG in New York.

Household formation can be a nebulous term, so it's ofteneasiest to explain it using examples. The CensusBureau defines a household as all the people living in a house orapartment -- or even a single room if it's intended to be usedas a separate living space.

A new household is formed if, for example,a person decides to move from his or her parents'home (also a household) into their own studio apartment. Or itcan occur when a couple who was living separately movesin together to a different home.

Tuesday's Census data show that the households beingformed these days are renters. Renter-occupied homes climbedby 1.87 million in the first quarter from a year ago, whileowner-occupied units fell by 386,000.

"This is positive for the economy," Harris said. "It would bebetter if they were buying instead of renting, but it still helpsif they're renting instead of living at home."

That's because these people have to fill their apartments withstuff -- coffee makers, televisions, bed frames from Ikea.While they'll probably be buying less than they would if they werenew homeowners, consumer spending should still get a nice boost,Harris said.

More people seeking apartments also puts upward pressure onrents. As that happens, it will make buying a home a morecompelling case for renters who have good enough credit to doso.

"There's an effect on homeownership and home sales down theroad," Harris said. "It's a plus for the economy."

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