In 2007, just prior to the Great Recession, 66.8 percent of non-elderly Americans had private insurance. By 2015, two years into the ACA’s expansion, that share had declined to 65.6 percent. Taking the larger economic picture into account by looking back to 2007 is crucial, because the private-insurance rate fluctuates with employment. Between 2007 and 2010, employment fell by 5.5 percent and private coverage fell by 7 percent. Between 2010 and 2015, employment rose by 8.8 percent and private coverage rose by 9.5 percent.

ACA implementation has coincided with an increase in private coverage because it occurred during a period of job growth. But 300,000 fewer Americans have private coverage today than would have it if the ratio of coverage to employment had remained at its 2007–10 level over the last six years.

Instead, the ACA has increased insurance coverage by expanding Medicaid. In 2007, 18.1 percent of non-elderly Americans had public insurance. By 2010, that share was 22 percent, and rather than declining as the economy recovered, it continued to climb all the way to 25.3 percent in 2015.

This public-versus-private distinction is crucial, because studies of Medicaid do not find the same positive effects on mortality sometimes seen in studies of private insurance. Researchers have found that Medicaid patients with a variety of conditions and medical needs experience worse outcomes than similar uninsured patients. In a randomized trial in Oregon that gave some individuals Medicaid while leaving others uninsured, recipients gained no statistically significant improvement in physical health after two years.