The economic impact of undocumented immigrants in the United States is challenging to measure, and politically contentious. Research shows that undocumented immigrants increase the size of the U.S. economy/contribute to economic growth, enhance the welfare of natives, contribute more in tax revenue than they collect, reduce American firms' incentives to offshore jobs and import foreign-produced goods, and benefit consumers by reducing the prices of goods and services. Economists estimate that legalization of the undocumented immigrant population would increase the immigrants' earnings and consumption considerably, and increase U.S. gross domestic product. Undocumented immigrant population According to the Pew Research Center, there were 11.3 million illegal immigrants living in the United States in 2016, statistically unchanged from the previous year. The number peaked at 12.2 million in 2007, following a steady increase that began in 1990. An estimated 5.6 million unauthorized immigrants were from Mexico in 2015 and 2016, down from 6.4 million in 2009. Non-Mexicans numbered 5.7 million, indicating Mexicans are no longer the clear majority of unauthorized immigrants. The U.S. civilian workforce includes 8 million unauthorized immigrants, accounting for 5% of those working or looking for work in 2014. This number has been relatively stable since 2007, ranging between 8.0 and 8.3 million. Unauthorized immigrants represent 26% of farming and 15% of construction labor. They are primarily concentrated in six states: California, New Mexico, Texas, Florida, New York, New Jersey, and Illinois. About two-thirds have been in the U.S. for more than a decade. The reduction has been driven mainly by a decrease in the number of new immigrants from Mexico, the single largest source. Net immigration from Mexico to the U.S. has stopped and possibly reversed since 2010. At its peak in 2000, about 770,000 immigrants arrived annually from Mexico; the majority arrived illegally. By 2010, the inflow had dropped to about 140,000—a majority of whom arrived as legal immigrants. At its peak in August 2007, the number of undocumented immigrants in the U.S. was 12.5 million. This decreased by 1.3 million to 11.2 million by July 2008 (11%) due to either increased law enforcement or fewer job opportunities. Based on the Department of Homeland Security estimates in 2009, unauthorized immigrant population living in the United States decreased to 10.8 million in January 2009. On the whole, between 2000 and 2009, the unauthorized immigrant population grew by 27 percent. Immigrants to the U.S. are concentrated at both the high