alt Hacker News> The Big Mac Index is a price index published since 1986 by The Economist as an informal way of measuring the purchasing power parity (PPP) between two currencies and providing a test of the extent to which market exchange rates result in goods costing the same in different countries. It "seeks to make exchange-rate theory a bit more digestible."[1] The index compares the relative price worldwide to purchase the Big Mac, the flagship hamburger sold at McDonald's restaurants.