They are using the World Bank purchasing power parity statistics as a starting point.
The Penn (university of Pennsylvania) World tables of purchasing power parity 7.0 has adjusted PPP as follows.
China is estimated at 11.3 to 11.6 trillion.
India is estimated at 4.15 trillion.
China has grown by about 10% in 2010 and would be 12.5 to 12.7 trillion.
India has grown by about 8% in 2010 and would be nearly 4.5 trillion.
They surveyed wealthy people to determine which cities were believed to be the most important and which would be the most important.
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