The number of uninsured adult Americans has declined significantly more in states that have expanded Medicaid and set up their own health care exchanges as a part of the Affordable Care Act, according to a new Gallup poll.

The uninsured rate fell 2.5 percentage points in the 21 states and District of Columbia that have expanded Medicaid and set up their own exchanges in the Health Insurance Marketplace, the survey found. In the 29 states that have done nothing or used only one of these options, the rate of uninsured fell just .8 percent.

The survey showed that Texas, which has rejected Medicaid expansion and relied on, had the highest uninsured rate as of March at 27 at 17 percent. Massachusetts (4.9 percent) and Hawaii (7.1 percent) had the lowest.

The Affordable Care Act became law in 2010, but many specifics continue to be debated at the state level. For example, Nebraska lawmakers recently voted down Medicaid expansion, while Utah is considering Medicaid expansion, but under revised, more flexible terms than what the Affordable Care Act provides. States like Montana and Louisiana may put the question of Medicaid expansion to voters on the November ballot.

Nationally, the uninsured rate peaked at 18 percent in the third quarter of 2013, but has declined to 15.6 percent. According to the Obama Administration, 8 million people have signed up for private health insurance using the online health insurance exchanges that opened in October. Another 3 million people have enrolled in Medicaid.

The law requires all but the poorest Americans to have insurance, while providing financial assistance for many to make the coverage affordable. Those who already have coverage through their employer or through Medicare, Medicaid or other public programs are not required to purchase new coverage through the Marketplace. Insurance through the Marketplace is available for people younger than 65 and legally living in the United States, as well as for business owners who employ fewer than 50 full-time people.

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