PLAINVIEW - A new census study has found that 1.6 million people moved out of New York over the past decade, about 100,000 of them from Long Island. Some Long Islanders weren't surprised to hear that more than 71,000 residents of Nassau and 35,000 residents of Suffolk left the area. "It's just a very expensive place to live," says Jeff Soloman, of Jericho.However, the study's co-author, Robert Scardamalia, of the Empire Center for New York State Policy, says the state isn't at risk of becoming depopulated. "Just because there's out-migration doesn't mean the state isn't growing," he says, citing rising birth rates and the arrival of foreign immigrants. Still, Larry Levy, of Hofstra University's Center for Suburban Studies, says local officials should be concerned because Long Island is losing younger and better-educated people, as well as older and more prosperous residents. According to the authors of the new study, the majority of those who left New York settled in southern and western states.