Research on the economic effects of undocumented immigrants is scant but existing studies suggests that the effects are positive for the native population, and public coffers. A 2015 study shows that "increasing deportation rates and tightening border control weakens low-skilled labor markets, increasing unemployment of native low-skilled workers. Legalization, instead, decreases the unemployment rate of low-skilled natives and increases income per native." Studies show that legalization of undocumented immigrants would boost the U.S. economy; a 2013 study found that granting legal status to undocumented immigrants would raise their incomes by a quarter (increasing U.S. GDP by approximately $1.4 trillion over a ten-year period), and a 2016 study found that "legalization would increase the economic contribution of the unauthorized population by about 20%, to 3.6% of private-sector GDP." A 2018 National Bureau of Economic Research paper found that undocumented immigrants to the United States "generate higher surplus for US firms relative to natives, hence restricting their entry has a depressing effect on job creation and, in turn, on native labor markets."