Because the performance ratio looks at the whole, rather than the sum of the parts, this indicator can take into consideration individual variables that are ignored by current metrics.

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The ratio of total wealth of the billionaires to gross domestic product (GDP) - an indicator of how extreme wealth compares with India's growth - rose from around 1% in the mid-1990s to 22% at the peak of the stock market boom in 2008, before dropping to 10% of GDP this year.

BBC: India's billionaires and the wealth of the nation

But the key here is that the ratio of outbound to inbound searches went up from 2011 to 2012, which is an early leading indicator that outbound migration might be accelerating, too.

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