"The states that have implemented two of the law's core mechanisms ... are realizing a rate of decline that is substantively greater than what is found among the remaining states that have not done so," Gallop wrote. "Consequently, the gap that previously existed between the two groups has now expanded."
Nationally, the uninsured rate has fallen from 18 percent before Obamacare enrollment launched in October to 15.6 percent in the first quarter of 2013.
The 2013 figures are based on a yearlong survey of 178,068 U.S. adults. The 2014 figures are based on a survey, conducted from January through March, of 43,562 U.S. adults.