What can a burger tell us about the global economy? More than you might imagine, according to The Economist, which is out with its Big Mac Index. The index reveals that, at market exchange rates, the price of the same McDonald’s (MCD) burger can vary vastly from country to country. The Big Mac costs $1.67 in India, $4.37 in the U.S., and $7.84 in Norway? Ryan Avent, chief economist at The Economis