NEW YORK

Despite rapid growth in the immigrant population, newcomers of the past quarter-century have assimilated more rapidly than their counterparts of a century ago, according to a conservative think tank.

However, the report from the Manhattan Institute indicates that Mexican immigrants are not assimilating as fast as other groups, a difference largely attributed to lack of legal status for many. Undocumented status, in turn, limits access to the means of assimilation.

The report, which uses U.S. Census Bureau data to calculate similarities between native and foreign-born adults in the United States, concluded that the degree of similarity has held steady since 1990 but was low by historical standards.

The report, “Measuring Immigrant Assimilation in the United States” by Dr. Jacob Vigdor, an associate professor of public policy studies and economics at Duke University, introduces a quantitative index  of the degree of similarity between U.S.-born and foreign-born adults. “It is the ability to distinguish the latter group from the former that we mean when we use the term ‘assimilation,’ Vigdor wrote in the executive summary.

In the index, immigrants are categorized by country of origin, date of arrival, age, and place of residence.

“The index reveals great diversity in the experiences of individual immigrant groups, which differ from each other almost as much as they differ from the native-born,” he said. “They vary significantly in the extent to which their earnings have increased, their rate of learning the English language, and progress toward citizenship. Mexican immigrants, the largest group and the focus of most current immigration policy debates, have assimilated slowly, but their experience is not representative of the entire immigrant population.”

In an article for The Boston Globe, Vigdor said many Mexicans do not have much incentive to assimilate because they strongly expect to return home and they can function in Spanish-speaking populations in the United States. In addition, those without legal status lack a path to citizenship and  better jobs.