The study measured the net change through March 31, when enrollment ended.
The uninsured rate fell by 2.7 percentage points, to 15.2 percent among adults 18-65. Unsurprisingly, the drop was greater in states that adopted Obamacare's Medicaid expansion -- by an average of 4 percentage points, versus 1.5 percentage points for states that declined the expansion.
The Urban Institute cautioned that the estimates "understate the full effects of the Affordable Care Act on the uninsured" by not fully capturing the late enrollment surge and omitting dependents who gained coverage under a parent's plan.
The institute illustrated the phenomenon in a chart: