The Big Mac Index is based on the theory of purchasing-power parity (PPP), which says that exchange rates should move to make the price of a basket of goods the same in each country.
The Economist's Big Mac Index, a light-hearted guide to how far currencies are from fair value, provides some answers.
It is so standardised that The Economist of London publishes an annual Big Mac Index to demonstrate the relative purchasing power of various currencies.
