《经济学人》精选:为什么说中国的汉堡还不够贵?

小编选注：
The Big Mac Index is published by The Economist as an informal way of measuring the purchasing power parity (PPP) between two currencies and provides 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".
The Big Mac PPP exchange rate between two countries is obtained by dividingthe price of a Big Mac in one country (in its currency) by the price of a Big Mac in another country (in its currency). This value is then compared with the actual exchange rate; if it is lower, then the first currency is under-valued (according to PPP theory) compared with the second, and conversely, if it is higher, then the first currency is over-valued.
两国的“巨无霸指数”计算法，是以一个国家的巨无霸以当地货币的价格，除以另一个国家的巨无霸以当地货币的价格。该商数用来跟实际的汇率比较；要是商数比汇率为低，就表示第一国货币的汇价被低估了（根据购买力平价理论）；相反，要是商数比汇率为高，则第一国货币的汇价被高估了。
举例而言，假设一个巨无霸在美国的售价为$2.50，在英国的售价为 £2.00；购买力平价汇率就是2.50 ÷2.00 = 1.25。如果当时汇率为£1 = $1.82，则表示以两国巨无霸的售价而言，英镑兑美元的汇价被高估了45.6%（(1.82-1.25)÷1.25×%）。
批评者认为，巨无霸汉堡包指数忽略了不同国家的税收、利润水平和原材料价格等因素的影响。

Purchasing power parity (PPP) is a theory of long-term equilibriumexchange rates based on relative price levels of two countries. The idea originated with the School of Salamanca in the 16th century and was developed in its modern form by Gustav Cassel in 1918. The concept is founded on the law of one price; the idea that in absence of transaction costs, identical goods will have the same price in different markets.
购买力平价（Purchasing Power Parity，简称PPP），又称相对购买力指标，是一种根据各国不同的价格水平计算出来的货币之间的等值系数，使我们能够在经济学上对各国的国内生产总值进行合理比较，这种理论汇率与实际汇率可能有很大的差距。
该理论指出，在对外贸易平衡的情况下，两国之间的汇率将会趋向于靠拢购买力平价。一般来讲，这个指标要根据相对于经济的重要性考察许多货物价格才能得出。