Giovanni Peri analyzes data for 2000-2009, when poverty rates increased significantly in the United States, and 1990-2000 as a comparison decade, to determine whether the presence of immigrants in the U.S. labor market has significantly affected the percentage of "poor" families among U.S.-born individuals. He finds that immigration has no effect on native poverty at the national level. At the local level -- that is, cities and states -- he does find some effects of immigration on poverty. However, even these local effects of immigration bear very little correlation with the observed changes in poverty rates. These effects also explain only a small fraction of the observed changes in poverty rates.That is from the NBER. The paper is here.