balassa-samuelson effect big mac big mac index cfa franc capital asset central bank china consumer price index cost currency diamond euro european union exchange rate exploitation foreign exchange market geary-khamis dollar gross domestic product gustav cassel hypothesis ipod india inflation inflation rate japan law of one price market basket mean measures of national income and output mexican peso penn effect price index price level purchasing power renminbi saving shipping speculation standard of living surplus switzerland tariff the economist tradable trade barrier united states united states dollar welfare economics wisconsin