Let people assume, for the sake of argument, that China's economy is on the verge of surpassing the US economy in size. By one measure, anyway -- purchasing power parity as calculated by the World Bank's International Comparison Program. What does it mean? It doesn't mean China is rich. On a per-capita basis, the highest-income country in the world in 2011 was the oil-soaked and lightly populated Gulf monarchy of Qatar, at $146,000 per person. The US was No. 12, at just under $50,000.