"Of the 11 states with the greatest reductions, 10 expanded Medicaid and established a state-based marketplace exchange or state-federal partnership," Gallup reported. "No state reported a statistically significant increase in the percentage of uninsured in 2014 compared with 2013."

To demonstrate the powerful one-two punch of Medicaid expansion and a state exchange, Gallup compared the average decrease for states with both factors against states with one or neither in play. The two-fers showed a decline from 16.1 percent uninsured to 11.3 percent, while the other groups reported an average decline of 2.7 percent, from 18.7 percent to 16 percent.

Other findings include:

• Massachusetts had the lowest uninsured rate at 4.6 percent, making it seven straight years the Bay State reported the lowest rate.

• Texas also made it seven straight years as the state with the highest uninsured rate (24.4 percent). The state's rate did drop almost 3 percent year over year.

• Uninsured rates were highest in the South and West, lowest in the East and Upper Midwest.

"States that have implemented two of the law's core mechanisms — Medicaid expansion and state health exchanges — are seeing a substantially larger drop in the uninsured rate than states that did not take both of these actions. Consequently, the gap in uninsured rates that existed between these two groups in 2013 nearly doubled in 2014," Gallup said.