WASHINGTON - A new study on emergency rooms disputes the common wisdom that the poor and uninsured are filling them up. In fact, more than 80 percent of patients seen in emergency rooms have health insurance and a usual source of health care such as a primary care physician, doctors reported on Tuesday. "Contrary to popular perception, individuals who do not have a usual source of care are actually less likely to have visited an emergency department than those who have such care," said Dr. Ellen Weber, an professor in the division of emergency medicine at the University of California...