The Romney campaign called the fund's portrayal of Romney's proposals inaccurate.

"The Commonwealth study sadly contributes little to the health reform conversation that this country deserves," Romney spokeswoman Andrea Saul told CNN. "It badly mistakes Gov. Romney's proposals. Worse, it assumes a fantasy world where Obamacare has been a success.  Instead, Americans have seen their insurance premiums increase, small businesses are facing massive tax increases and seniors will have reduced access to Medicare services."

Commonwealth authors admit that since Romney's proposals haven't been specified, "a set of assumptions was made" for the report based on similar proposals advanced in the past.

Romney has said he would repeal the health reform law, but still keep some of the law's more popular provisions in place.

It's the second report in just a week that argued Americans would be worse off without the PPACA and under Romney's health care plan.

A report from Washington, D.C.-based consumer advocacy group Families USA last week claimed that families buying non-group health insurance on their own in 2016 would pay nearly twice as much under the health proposals offered by Romney than under Obama's health reform law.

The Commonwealth Fund, a liberal think tank that supports research on health care issues, compared the candidates' health care plans by looking at seven key issues: health insurance coverage, insurance affordability, consumer protection, consumer choice, help for small business, improving Medicare, and improving health care quality and slowing spending growth.

The analysis was conducted by economist Jonathan Gruber, who advised the policymakers who wrote the PPACA.

The report claims people in southern and western states would benefit significantly from the PPACA. By 2022, when the law is fully implemented, uninsured rates are estimated to fall by more than 15 percentage points in 11 states. Health reform would also reduce the uninsured rate from to 10 percent to 15 percent in 13 states across the South and West, as well as in New York and the District of Columbia, and to less than 10 percent in the rest of the states, the report claims.

The study also found that Romney's plan would cost Americans more money. People who choose to buy health insurance on their own would pay 14 percent of their income, compared to only 9 percent under the PPACA, The Commonwealth Fund says.

Cost has been a major point of contention, with both Romney and insurance insiders saying health reform will increase costs. Research from global insurance broker Willis Group Holdings earlier this year confirmed that health costs continue to rise, and that the PPACA is one of the significant reasons for the cost increases. In turn, employers are asking their employees to pay more for coverage.

Health insurers have long questioned the "affordable" part of the PPACA, saying the law doesn't address the key problem of cost and affordability.

"While the Supreme Court's decision about the Patient Protection and Affordable Care Act determined the outcome of one of the most significant judicial cases of the century, no one has yet addressed one of the most pressing issues facing our nation: the rising cost of health care," Digital Insurance President and CEO Adam Bruckman said in June. "Our country still does not have measures in place to control a system that is on an unsustainable cost trajectory. If we are to effect meaningful change, we are obligated to devise methods to curb rising expenses."