In the history of the Big Mac index, the dollar has never been more overvalued CURRENCY forecasters have had it hard in recent years. Most expected the euro to rise after its launch in 1999, yet it fell. When America went into recession last year, the dollar was tipped to decline; it rose. So to help forecasters really get their teeth into exchange rates, The Economist has updated its Big Mac index. Devised 16 years ago as a light-hearted guide to whether currencies are at their “correct” level, the index is based on the theory of purchasing-power parity (PPP). In...