Big increases in immigration since 1990 have not hurt employment prospects for American workers, says a study released Thursday. The report comes as Congress and much of the nation are debating immigration policy, a big issue in this fall's midterm congressional elections. The Pew Hispanic Center found no evidence that increases in immigration led to higher unemployment among Americans, said Rakesh Kochhar, who authored the study. Kochhar said other factors, such as economic growth, played a larger role than immigration in setting the job market for Americans. The study, however, did not look at whether wages were affected by immigration....