Commuters to New York City play an outsized economic role on Long Island, according to a report the Island's largest business group plans to release Wednesday.

Nearly one-fifth of Long Islanders worked in the city in 2013 and earned wages that accounted for nearly two-fifths of all local residents' earnings that year, said the Long Island Association study.

"Our two economies are linked; our work forces are linked," said the group's president, Kevin Law.

The report is the first such study since the Long Island Regional Planning Board's 1995 report, Law said. The LIA hopes to use the data to press for more funding to improve the Long Island Rail Road, which the group considers vital to the Island's economic growth.

"It will arm us with ammunition to advocate for state and federal funding," Law said.

The number of Long Island workers who commute to the city rose by just 10,400 between 1990 and 2013, to about 279,100, said the study, which was done by the LIA's Research Institute. Meanwhile, their representation dipped to 18.7 percent of Long Island workers in 2013, from 19.1 percent in 1990.

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Still, their wages accounted for 39 percent of all wages Long Island residents earned between 2011 and 2013, or about $27.4 billion. Those workers' salaries then generated another estimated $25 billion through the multiplier effect of local consumer spending.

In Nassau, commuters' percentage of all wages was 56.9 percent, compared with 21.4 percent in Suffolk.

"It shows that Long Island continues to get the benefit of being in the shadow of New York City," said Lawrence Levy, executive dean of Hofstra University's National Center for Suburban Studies.

He said that after a generation when Long Island became less dependent on the city for growth, it may become more reliant because the city's recent "explosive" job and wage gains far outpaced Long Island's.

Local residents who commute to New York City to work, especially to Manhattan, bring home bigger paychecks. For example, the annual salary of a Long Island resident who commuted to Manhattan averaged $118,223 between 2011 and 2013, compared with $88,083 for inter-Long Island commuters.

"The higher-income earners are largely commuting to the city," said Martin Melkonian, an associate professor of economics at Hofstra. "There aren't that many high-wage businesses on Long Island, particularly in the finance industry."

To be sure, the city also benefits from its proximity to the Island, the experts said. Law noted that Long Island companies rely on New York City residents to fill jobs.

The LIRR is considered key to that interdependency. Long Island residents who commute to the city via the LIRR account for 34 percent of daily work trips between those areas."Improving access to and from New York City can strengthen both the Long Island and New York City economies," the report said.