In 2012, the Supreme Court ruled the Affordable Care Act could not mandate each state to expand Medicaid eligibility. That decision, in effect, created a nationwide experiment to see how uninsured rates would change when states opened up the program to more low-income people.

The bottom line: States that didn't expand Medicaid have much higher uninsured rates compared with states that expanded Medicaid, according to the latest Census Bureau data. Hospitals and doctors in Medicaid expansion states consequently recorded more patient visits, although that has tapered off.

Newsworthy: Texas and Florida, states that did not expand Medicaid and are grappling with the aftermath of two massive hurricanes, have two of the highest uninsured rates in the country (16.6% in Texas and 12.5% in Florida).