Dating game

FORGET Monopoly or World of Warcraft. The Economist's idea of Christmas fun is guessing when China's economy will leapfrog America's to become the world's biggest. The Conference Board, a business-research group, recently predicted that China could become the world's largest economy as soon as 2012 on a purchasing-power-parity (PPP) basis, which adjusts for the fact that prices are lower in China. But economists disagree on how to measure PPP. And America will only really be eclipsed when China's GDP outstrips it in plain dollar terms, converted at market exchange rates.

Since by that reckoning China's GDP is currently only two-fifths the size of America's, that day may still seem distant. But it is getting closer. When Goldman Sachs made its first forecasts for the BRIC economies (Brazil, Russia, India and China) in 2003, it predicted that China would overtake America in 2041. Now it says 2027. In November Standard Chartered forecast that it will happen by 2020. This partly reflects the impact of the financial crisis. In the third quarter of 2010 America's real GDP was still below its level in December 2007; China's GDP grew by 28% over the same period.