Since open enrollment for the health insurance exchanges began in October 2013, millions more Americans have received coverage and their access to care and self-reported health have improved, according to an analysis of telephone surveys conducted in the past two years.

Lead researcher Benjamin D. Sommers, MD, PhD, said the passage of the Patient Protection and Affordable Care Act has led to the largest reductions in the uninsured rate in more than 40 years. He pointed to three factors: children can stay on their parents’ coverage until they turn 26; the creation of the exchanges; and the expansion of Medicaid. Sommers and his colleagues published their results online in JAMA on July 28.

The researchers examined the Gallup-Healthways Well-Being Index, a telephone survey of adults living in all 50 states and the District of Columbia. They included data from January 2012 through March 2015 and evaluated 507,055 adults who were between 18 and 64 years old.

To determine how much of a factor the ACA provisions were in the improved health and other outcomes, the researchers controlled for economic factors such as employment rates and incomes.

“That gives us pretty good confidence that major changes in the economy aren’t driving these results,” Sommers, a health economist and a primary care physician at Brigham and Women’s hospital in Boston, said in a conference call. “Could there be other factors that were not measured or that aren’t obvious? Of course. With a policy like the ACA, we’re never going to have a randomized trial that gives us that kind of slam dunk case, but we’re going to do the best we can looking at these trends with the information we have.”

As of March 2015, 11.7 million people signed up for coverage through the marketplaces and 12.2 million more people had enrolled in Medicaid and the Children’s Health Insurance Program compared with mid-2013.

The marketplaces were created as part of the ACA, open enrollment began in October 2013 and coverage began in January 2014. The study included two groups: pre-ACA expansion (January 2012 to September 2013) and post-ACA expansion (January 2014 to March 2015).

In the post-ACA expansion era, the uninsured rate fell by 7.9 percentage points, which Sommers said converts to an additional 15.8 million adults receiving coverage. He added that seven million more adults gained access to a personal physician, 4.8 million more adults gained access to medicines, 11 million more adults indicated they could afford healthcare and 6.8 million more adults said they were in excellent, very good or good health.

Sommers said the most significant improvements in care occurred in racial and ethnic minorities. For instance, approximately 4.1 million Latino adults gained insurance since January 2014 and an additional 1.1 million black adults reported improved access to medicines.

The researchers also found states that expanded Medicaid had significant reductions among low-income adults in the uninsured rate and significant increases in people with personal physicians and their access to medicines.

Among adults with at least one chronic condition such as diabetes, cancer or heart disease, the researchers found significant improvements in self-reported health and reductions in health-related limitations.

“Overall we are basically getting with this data set and with this analysis a 10,000-foot view of what’s happening in these broad patterns of access to primary care and medications, of affordability and health,” Sommers said. “We’ll need additional data sources to look at what are the medications people are taking, what are the conditions that are being treated, how are the outcomes of those conditions improving? This is what we see as a first step in gauging the impact of the ACA on these trends. Much more work will be needed after this.”