A new study says that undocumented immigrants play a critical role in Minnesota's economy. The study was sponsored by a Hispanic advocacy group and supported by the University of Minnesota's Center for Urban and Regional Affairs. Researchers estimate that undocumented workers contribute 3.8 billion dollars to the state's economy each year. Jim Kielkopf is an economist and the author of the study. He says his numbers are based on interviews with insiders in several key industries.