The study found that the uninsured rates dropped in every state, but that there were some particularly large decreases in the uninsured rates for low-income adults in states that expanded Medicaid under the law. (States were given the option to opt-out of Medicaid expansion with a 2012 Supreme Court decision, and many red states have chosen to do so).
"Nine such states experienced 10 to 13 percentage-point reductions in their adult uninsured rate from 2013 to 2015. Six of these states—California, Kentucky, Oregon, Rhode Island, Washington, and West Virginia—sliced their uninsured rates by at least half over the two years," the report said.
The study also examined how the uninsured rates have changed under the ACA with regards to the disparities between white and black or Hispanic communities. Between 2013 and 2015, there were significant coverage gains made among those minority groups: the national uninsured rate dropped to 15 percent from 24 percent among black adults and to 28 percent from 40 percent among Hispanic adults. But here too, states' decision to expand Medicaid played a crucial role.
"In states that expanded Medicaid as of January 2015, the average uninsured rate for nonelderly black adults was 11 percent compared to 19 percent in states that did not expand," the report said. "For Hispanics, the difference was even greater: the average uninsured rate was 22 percent in states that expanded Medicaid and 36 percent in states that did not."
The study comes as Republicans are plotting their moves to repeal Obamacare without a replacement, which they say they'll come up with in a two- to four- year transition phase. It is unclear whether GOP lawmakers will seek in their ACA alternative to match Obamacare's achievements in coverage access.