NPR's Legal Affairs Correspondent Nina Totenberg reports the Supreme Court will begin hearings on an important case that will help determine how the next U.S. census will be taken. At the heart of the matter is whether limited use of sampling is constitutional. Democrats and statisticians claim the present census is inaccurate, undercounting the population by 4-8 million people, most of whom are poor. They say sampling helps account for those who are missed by usual headcounting methods. Republicans and conservatives are fighting it. They claim the Constitution requires an actual person-by-person headcount.