Family-based migration is a huge “multiplier” of overall immigration levels, especially for a handful of countries including Mexico and China, according to a Center for Immigration Studies (CIS) report released Wednesday.

The report quantifies the role of chain migration in the U.S. immigration system.

Over the last 35 years, chain migration has greatly surpassed new immigration by what are known as “initiating immigrants,” or the first in their family to settle permanently in America. Of the 33 million legal immigrants admitted to the U.S. from 1981 to 2016, about 20 million — 61 percent — were chain migration immigrants, according to the report written by Jessica Vaughan, CIS director of policy studies.

To a greater degree than nearly all developed countries, U.S. immigration law allows recent immigrants — both legal permanent residents and naturalized citizens — to petition for immigrant visas for family members living overseas. Green card holders can sponsor spouses and children, and naturalized citizens can sponsor those same relatives plus parents, siblings and married adult children.

The system creates an interconnected web of relatives who are eligible to immigrate to the U.S. from a single person. In theory, an entire extended family within the span of two generations could join a recent immigrant.

Immigrants from all countries use family-based visas to bring their relatives with them, but some nationalities are especially prolific in family sponsorship.

Of all the immigrant-sending countries, Mexico has the highest rate of chain migration, the CIS report found. In the most recent five-year cohort of immigrants studied — people who arrived between 1996 and and 2000 — each new Mexican immigrant sponsored an average of 6.38 family members.

Immigrants from China were not far behind: Each initiating Chinese immigrant led to an additional 6.24 family members. Other nationalities with high chain migration multipliers are India and the Philippines, with 5.11 and 5.07 additional immigrants, respectively.

Those high multipliers are stark examples of a long-term trend: Recent immigrants are sponsoring more family members than earlier cohorts. Immigrants who arrived between 1981 and 2000 each sponsored an average of 1.77 additional immigrants, Princeton researchers found in a 2013 study. But within the group who came to the U.S. between 1996 and 2000, the average was 3.46 people.

The propensity of recent immigrants to sponsor more family members is one reason why overall legal immigration levels have reached recent highs. Legal immigration in 2016 was approximately 1,125,000 — 7 percent higher than 2015 and one of the highest annual totals since 1990, Vaughan notes.

High levels of chain migration have taken on greater salience amid the fight over a potential amnesty bill for Deferred Action for Childhood Arrival (DACA) recipients. Without changes to chain migration laws, immigration hawks say a clean amnesty bill would result in a surge of legal migration far larger than the DACA-eligible population. Giving legal permanent residence to 700,000 DACA beneficiaries would likely double that number in additional immigrants, according to Vaughan’s report.

Conservative immigration reformers have long argued that the system of chain migration allows too many low-skilled relatives to immigrate legally and compete with native-born workers for a dwindling share of jobs. Some Republican lawmakers have proposed moving to a skills-based system that would cut legal immigration levels by nearly half over a decade, largely by placing limits on the types of family members that could be sponsored for immigrant visas.

Thus far, Republican proposals to legalize DACA recipients have not touched on reforms that would curtail chain migration among the overall immigrant population. A recent bill from GOP Sens. Thom Tillis of North Carolina and James Lankford of Oklahoma would prevent amnestied immigrants from petitioning for family members during a 15-year naturalization period.

The so-called SUCCEED Act, however, allows the participants to sponsor relatives after they become U.S. citizens.

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