"Welcome back" are two words you'd really rather not hear at a hospital, especially if you've just been discharged. Yet one in five Medicare patients found themselves back in the hospital within 30 days of leaving it in 2003 and 2004, according to a recent study in the New England Journal of Medicine. Even more troubling is the possibility that three-quarters of those readmissions might have been prevented, as estimated in a 2007 report by the Medicare Payment Advisory Commission, an independent agency that advises Congress. What gives? All too often, experts, say, the problems that send patients back to the hospital might have been avoided if there had been a better handoff from the hospital to the people responsible for the next phase in a patient's recovery.