The latest IMF forecast report is here (World Economic Outlook
April 2011, 242 pages)
Under PPP, the Chinese will expand from $11.2 trillion this year to $19 trillion in 2016. Meanwhile the size of the U.S. economy will rise from $15.2 trillion to $18.8 trillion. That would take America’s share of the world output down to 17.7%, the lowest in modern times. China’s would reach 18%, and rising.
The Conference board predicted that China will pass the USA in 2012
The Peterson Institute finds that China passed the USA economy on PPP in 2010