Middle-class minority households are a big factor in gentrification, a new study shows, and the families that move into gentrifying neighborhoods see their incomes grow.

Using U.S. Census data, the study examined urban neighborhoods across the country with average family incomes of less than $30,000 in 1990. Of those neighborhoods, it then called “gentrifying” those that saw average income increase at least $10,000 between 1990 and 2000.

While the conventional wisdom is that gentrification displaces minority residents, the study found that more middle-income minorities were attracted to the gentrifying neighborhoods, especially college-educated black families with children ages 20 to 40, and Hispanics ages 40 to 60 of most education levels.

In particular, black high school graduates remained in neighborhoods that were gentrifying, the study found, and their average incomes increased 20% more in gentrifying neighborhoods than in non-gentrifying neighborhoods.

“The study shows that, on average, the displacement patterns some people are concerned about were not happening,” one of the study’s authors, Randall Walsh, said.

Mr. Walsh, an assistant professor of economics at University of Colorado at Boulder, published the study last month with Terra McKinnish, also of the University of Colorado, and Kirk White of Duke University.

Although the data showed that minorities are not always pushed out of areas that are gentrifying, the numbers are averages and do not apply to all situations, the authors said.

The study “certainly does not mean that in certain areas that displacement isn’t happening,” Mr. Walsh said. “But it does provide some evidence that, on average, this is not as big of a concern.”

Community advocates questioned the conclusions of the study.

“Low-income communities, especially communities of color, are being hard hit by gentrification in New York City,” the director of research policy at the Community Development Project of the Urban Justice Center, Laine Romero-Alston, said. “The black community in Harlem is clearly facing issues of displacement and other issues with gentrification, like substandard living.”

Still, the study underlines that many communities do benefit from the changes, the chairman of the sociology department at New York University, Dalton Conley, said.

In neighborhoods where residents own homes, they can turn a profit if they want to sell their properties to wealthier people seeking to move in, he said. “Even if gentrifiers develop plots that are abandoned, and the people next door own their homes, their property value goes up.”

Small local businesses also can benefit from the changes, Mr. Conley added.

“Our results show that for the groups that you would expect to see displacement, we did not see evidence that they were moving out of houses at a higher rate than they move out of neighborhoods that were not gentrified,” Mr. Walsh said.