A wide-ranging and provocative new study of immigrants' integration into U.S. society has concluded that newcomers today are assimilating more quickly than their predecessors did 100 years ago -- with Cubans, Vietnamese and Filipinos among those leading the way.

The study, conducted by Duke University economist Jacob L. Vigdor and published Tuesday by the Manhattan Institute, a free-market-oriented conservative think tank in New York City, seeks to break new ground on one of the most contentious topics in the debate over immigration -- the question of how the record-setting immigrant stream of the past 25 years is jelling with its sometimes wary host.

The study's answer: remarkably well, with some worrisome exceptions.

Mexicans -- by far the most numerous nationality -- lag significantly behind other big immigrant groups, possibly because a lack of legal status keeps many from advancing.

''The bottom line is there are some encouraging things and some things to be concerned about, but the nation's capacity to integrate new immigrants is strong," said Vigdor.

The study can be found online at manhattan-institute.org

The study, based on U.S. Census Bureau and survey data, considered assimilation as of 2006 on three fronts -- economic, cultural and civic -- and assigned each immigrant group a number ranging from zero to 100 that indicates how similar its members are to native-born Americans. The higher the number is, the more assimilated the group.

The study -- "Measuring Assimilation in the United States" -- is meant to aid the immigration debate and deliberately makes no recommendations, Vigdor said in a phone conference Monday.

The report's overall findings are consistent with other research on immigrant integration, said Michael Fix, vice president of the Migration Policy Institute, a research group in Washington.

But it's a complex and nuanced analysis that could be misconstrued, Fix said. And other research, including studies done by MPI, have found better results for Mexican immigrants' economic advancement, especially for the second generation, he said.

"Other research in the main corroborates the main finding, that integration is proceeding apace," Fix said. "It's moving at different speeds for different groups."

The study found that today's newcomers are at this point less integrated than their counterparts 100 years ago. That's likely because those immigrants a century ago were largely European, with one of the largest groups coming from England, and thus started out with cultural and economic levels closer to that of native-born Americans.

By contrast, today's newcomers, who are mostly from Asia and Latin America, start off further behind, Vigdor said.

But today's immigrants are making faster progress. As a result, even as immigration has skyrocketed, assimilation has remained stable, Vigdor concluded. "This is something unprecedented in the United States," he said.

Immigrants are integrating rapidly on the economic and civic fronts -- that is, in terms of income, education and naturalization, and military service, among other factors. But they are doing so more slowly in cultural terms -- in learning English and intermarrying with the native-born.

That may in part reflect the difficulty immigrant adults have in learning English, as well as pressures among the newly arrived to marry within their group, Vigdor said.

Immigrants who arrive as small children rapidly erase those differences, the study found. Children who arrive before age 5 become virtually indistinguishable from native-born children along economic, cultural and civic lines as they grow into adulthood -- with the exception of Mexicans.

Immigrants from Cuba, Vietnam and the Philippines enjoy some of the highest rates of assimilation.