The Patient Protection and Affordable Care Act, better known as Obamacare, has inspired plenty of controversy ever since it became law. With the headaches involved in signing up for coverage using the recently opened health-insurance exchanges, residents in different states are having much different experiences with Obamacare and its efforts at reforming health insurance.

Most of the attention surrounding the Affordable Care Act has hinged on subsidies to buy insurance under the exchanges. But as a recent study from the Urban Institute and the Robert Wood Johnson Foundation found, Medicaid expansion under Obamacare could prove equally vital in providing assistance to uninsured Americans. The combination gives the following five states the highest proportion of uninsured residents who could become eligible for insurance assistance under Obamacare next year.

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Kentucky, 81%
In Kentucky, Gov. Steve Beshear embraced Medicaid expansion, allowing low-income individuals and families with incomes of up to 138% of the federal poverty line to become eligible for Medicaid. Beshear cited studies saying that Medicaid expansion would help more than 300,000 uninsured Kentucky residents get health care, creating thousands of jobs and having billions of dollars of positive economic impacts annually. In addition, Kentucky's insurance exchanges have gotten attention from big insurers, as UnitedHealth Group (NYSE:UNH), Humana (NYSE:HUM), and WellPoint's (NYSE:ANTM) Anthem are all providing coverage there.

West Virginia, 81%
Early reports showed that more than 50,000 West Virginians signed up for Medicaid in the first week of the launch of Obamacare health-care exchanges. Although the state's Medicaid website led to about 2,000 signups in the first week, most of those 50,000 signed up through auto-enrollment in the weeks before the marketplace became available. West Virginia expects the expansion to give 277,000 residents government-sponsored health coverage in the next three years.

Michigan, 81%
Michigan's expansion of Medicaid came as a political surprise to many, as many Republican-controlled states have chosen not to accept Medicaid-expansion funding from the federal government. But Gov. Rick Snyder and Michigan's Republican-controlled legislature approved Medicaid expansion in September, citing savings of $206 million in the next fiscal year and extending health-care coverage to 470,000 state residents. Still, Michigan chose to delay expansion until next spring, which could cost the state $630 million in federal funding.

North Dakota, 79%
In April, North Dakota approved Medicaid expansion to give assistance to 20,000 state residents. That doesn't sound like many, but in a state with a population of only 700,000, the number represents a big proportion of the state's uninsured, boosting the total number of people eligible for Medicaid by almost a third. Many state lawmakers said they were reluctant to support the expansion but said that added costs for residents if they didn't led them to move forward.

Hawaii, 77%
Hawaii has worked hard not just to pass Medicaid expansion but also to educate the public about its health-insurance marketplace. Hawaii spent more than any other state on public health-insurance education, with costs averaging to $67.54 for every uninsured resident under age 65. Those vigorous outreach efforts are aimed at making sure anyone who's eligible can take advantage of the program.