The number of uninsured working-age adults fell by 16.9 million between September 2013 and February 2015, to 25.8 million, according to a survey by RAND Corporation published online today by Health Affairs. Based on a nationally representative panel of 1,589 adults, the survey tracked insurance transitions over a period marking shortly before and after the first two open enrollment periods for the Affordable Care Act’s Health Insurance Marketplace. “The ACA has greatly expanded health insurance coverage in the United States with little change in the source of coverage for those who were insured before the major provisions of the law took effect,” the authors conclude. “Furthermore, the law has expanded coverage using all parts of the health insurance system, including employer-sponsored insurance, Medicaid and the newly created Marketplaces. While these data have limitations, especially due to the low response rate, they provide an early look at how the ACA has affected insurance enrollment.”