LOS ANGELES » The continuing economic downturn has drastically altered the internal migration habits of Americans, turning the flood of migrants into the Sun Belt and out of states like New York, Massachusetts and California into a relative trickle, an analysis of recent federal data confirms.

Essentially, millions of Americans have become frozen in place, researchers say, unable to sell their homes and unsure they would find jobs elsewhere anyway.

An analysis of new data from the Census Bureau and the Internal Revenue Service by the Carsey Institute at the University of New Hampshire confirms earlier census assessments of a migration slowdown but also offers a deeper, state-by-state look at the impact of this shift, which upends, however temporarily, a migration over decades to the sunny South.

The institute’s study compared three years worth of data from the Census Bureau’s American Community Survey, which was released Thursday and covered 2008-10, with the data from 2005-7. Since the survey’s findings are released in three-year increments, this was the first time that researchers had a set of data that included only years since the financial collapse began, allowing them to make a direct comparison to a similar period before the collapse.

Using this and other data from the IRS that many researchers consider even more comprehensive, they found that migration into formerly booming states like Arizona, Florida and Nevada began to slow as soon as the recession hit and continued to shrink even into 2010, when many demographers expected it to level off. At the same time, Massachusetts, New York and California, which had been hemorrhaging people for years, and continued to do so in the three years before the financial collapse, suddenly saw the domestic migration loss shrink by as much as 90 percent.

Mobility always tends to slow in times of economic hardship, and there has been a gradual decline in U.S. mobility for decades. But census numbers released earlier this year showed that domestic migration in 2010 had plummeted substantially since the recession began and reached the lowest level since the government began tracking it in the 1940s.

"When times get really hard it gets really hard for people to up and move," said Kenneth M. Johnson, the senior demographer at the Carsey Institute, who conducted the analysis. "People who might have left New York for North Carolina are staying put. But that is a very recent change, so that places that had been growing rapidly suddenly aren’t and the outflow has really slowed down."

Johnson said that the same phenomenon could be seen within states, as the growth begins to slow in once rapidly growing suburbs, while shrinking cities like Los Angeles and Chicago began to stabilize.

In the past three years, Florida saw its first net migration loss since the 1940s, according to the analysis. According to IRS data, the state had a net migration gain of 209,000 in 2005 but a loss of 30,000 in 2009.

Nevada’s strong migration gains flipped to a net loss of 4,000. Arizona scraped by, ending the decade with a 5,000 net gain, down from 90,000 five years earlier. Maricopa County in Arizona, home to Phoenix, and Clark County in Nevada, home to Las Vegas, two areas that had exploded with growth at the start of the decade, began to see more people move out than move in.

On the other hand, New York had a net loss of 71,000 migrants in 2009, substantially fewer than the 170,000 migrants it lost in 2005. California saw its loss of migrants shrink to 71,000 in 2009, down from 201,000 in 2005.

The IRS data covered the period through the 2009 tax year, but offered a detailed picture of the country in April 2010, when many returns were filed.

The internal migration data does not include those who came to states from other countries or the natural increase of the population through births. Those changes are major drivers for overall population growth and continued to make the Sun Belt and Western states the biggest population gainers of the decade. And young people, who have long been the most reliable group of new migrants to cities, also appear to be less willing to move to the cities within the Sun Belt.

In an analysis of the American Community Survey data made public Thursday, William Frey, a senior demographer at the Brookings Institution, found that large metropolitan areas with once-flourishing economies, like Atlanta, Phoenix and Riverside, Calif., are no longer magnets for Americans ages 25 to 34.

"These places that were getting real new interest amid the bubble are not seeing that anymore and in a way it is making people give another place a second look," Frey said. "The dynamics of high housing costs on the coasts and relatively affordable inland is starting to change so, in effect, that shuts off the merry-go-round.

"If nobody can buy or sell their homes, there’s going to be a stagnancy," he added.

Atlanta, which ranked third as a destination for young people in that age group from 2005 through 2007, sank to No. 23 in the period from 2008 through 2010, according to Frey’s analysis. Phoenix dropped to No. 17 from second place, and Las Vegas plummeted to No. 35 from 10th place.

The winners were cities like Washington, which skyrocketed to sixth from 44th, Denver, which jumped to first from 12th, and Boston, which is now No. 26, up from No. 45.

Frey said that, in many ways, young people are staying in the more established cities with a kind of wait-and-see approach to the economy. He said he expected the relocation rates to pick up as soon as there were new housing and job opportunities for young adults.

"They are trying to bide their time in a hip place they know," he said. "But there is going to be a pent-up demand for migration, because right now people are just putting their lives on hold."

© 2011 The New York Times Company