The United States may boast the largest economy in the world, but it's not the most competitive.

America's $15.7 trillion economy is No. 3 in competitiveness, trailing Switzerland and Singapore, according to a recent ranking by the World Economic Forum.

It's the sixth year in a row that Switzerland tops the list, the Geneva-based group said. Singapore has been a top contender for four years running.

While the U.S. came in third, the country has been moving up the ranks in recent years. In 2013, the U.S. economy was the fifth-most competitive global economy.

The forum said improvements in America's "institutional framework" and a more positive view of the nation's "business sophistication and innovation" helped boost its competitiveness score.

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In addition, the group said U.S. companies benefit from an "excellent university system" that works well with the private sector in research and development.

The forum measured the competitiveness of 144 nations based on a dozen categories, including institutions, infrastructure and education. It also looked at such things as market and labor efficiency, technology and innovation.

"The leading economies in the index all possess a track record in developing, accessing and utilizing available talent, as well as in making investments that boost innovation," the group said in a statement.

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However, the forum warned that more "structural reforms" are needed to keep the global economic recovery going.

It said central bank policy has helped support global growth in the years since the financial crisis and Great Recession. But governments have made "uneven" progress on reforms designed to boost competitiveness, the report states.

Greece was the world's least competitive economy. Other European countries that were hit hard in the euro crisis also scored poorly, including Italy, Cyprus, Slovenia and the Slovak Republic.