Expanding health insurance coverage for the poor leads to a significant increase in costly emergency room visits, according to a new study. The finding, published Thursday in the journal Science, raises the possibility of trouble ahead as millions of people gain health insurance through expansion of Medicaid under the new health care reform law, coverage that began kicking in on Wednesday. The 18-month study followed 25,000 low-income Oregonians who won Medicaid coverage in a lottery as part of the Oregon Health Insurance Experiment, a major policy research initiative. Researchers observed a 40 percent increase in emergency room visits among the...