The index is based on the idea of purchasing-power parity (PPP), which says currencies should trade at the rate that makes the price of goods the same in each country.
THE Big Mac index is based on the theory of purchasing-power parity (PPP)—exchange rates should equalise the price of a basket of goods in different countries.
巨无霸指数基于购买力平价理论，该理论认为汇率应该使不同国家的一揽子商品的价格相等。
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The Big Mac index is based on the theory of purchasing-power parity (PPP), according to which exchange rates should adjust to equalise the price of a basket of goods and services around the world.