WASHINGTON (Reuters) - A third of Americans say they have gone without medical care or skipped filling a prescription because of cost, compared to 5 percent in the Netherlands, according to study released on Thursday.

A doctor puts his hand over his chest during a "House call" rally against proposed healthcare reform legislation at the Capitol in Washington November 5, 2009. REUTERS/Kevin Lamarque

The study is the latest in a series by the non-profit Commonwealth Fund showing that while Americans pay far more per capita for healthcare, they are unhappier with the results and less healthy than people in other rich countries.

The study published in the journal Health Affairs also showed that 20 percent of U.S. adults had major problems paying medical bills, compared with 2 percent in Britain and 9 percent in France, the next costliest country.

“U.S. adults were the most likely to incur high medical expenses, even when insured, and to spend time on insurance paperwork and disputes or to have payments denied,” the report reads.

The Commonwealth Fund, which advocates for U.S. healthcare reform, commissioned a Harris Interactive poll of nearly 20,000 people in 11 countries between March and June.

“What we are hearing directly from adults around the world, and what we hear regularly at home, is that there is substantial room for improvement in the U.S. health insurance system,” said Commonwealth Fund President Karen Davis.

Healthcare reform was U.S. President Barack Obama’s signature policy effort, but not a single Republican voted for the bill that Obama signed into law this year and conservatives in Congress have promised to try to dismantle it.

The new law is meant to address some of the weaknesses in the U.S. system by forcing more Americans to buy health insurance, expanding public insurance and preventing insurers from dropping coverage.

About 60 percent of Americans under 65 get health insurance through an employer -- about 157 million adults. Health insurers include WellPoint, Aetna Inc, Cigna Corp, Humana Inc, UnitedHealth Group Inc, Health Net Inc, Amerigroup Corp and the Blue Cross Blue Shield network.

Roughly 45 million people 65 and older have coverage through the nation’s Medicare program for the elderly and disabled.

The system leaves 47 million without any health insurance, and last week the U.S. Centers for Disease Control and Prevention estimated that 59 million Americans had no insurance for at least some of the beginning of 2010.

The 10 other countries in the survey -- Australia, Britain, Canada, France, Germany, the Netherlands, New Zealand, Norway, Sweden and Switzerland -- all provide a mix of public and private insurance.

Adults in Britain, Switzerland, New Zealand and the Netherlands were the most likely to be able to get to a doctor the same day or next day when they needed to, the survey found.

More than 90 percent of Swiss adults said they could see a doctor that fast, compared with 57 percent of adults in Sweden and the United States, and fewer than half in Canada and Norway.

Only 70 percent of adults in the United States or Norway said they were confident they would get the most effective treatment if ill, compared with 90 percent of Britons and 89 percent of the Swiss.

“The United States is the only country in which one-fifth of adults reported serious problems paying health care bills,” the study adds.