Cologne, May 27 dpa – The U.S. dollar is undervalued against the Deutsch-mark based on how many Big Mac hamburger sandwiches the two currencies can purchase, said one of Germanys leading institutes.

The Institute of the German Economy (IW) in Cologne noted that the popular sandwich by the McDonalds restaurant chain is increasingly being used by economists around the world as a measure of currencies relative purchasing power.

The institute said that currency exchange rates are often unreliable as an instrument to measure purchasing power. At the same time, baskets of products used to arrive at comparative purchasing power are complicated to compile.