比如2013年中国GDP是1000，000人民币，这个GDP如何换算成1990年的盖凯美元呢。
希望能有具体的换算过程~


关于盖凯美元在维基和百度上的解释分别如下：


The Geary–Khamis dollar, more commonly known as the international dollar, is a hypothetical unit of currency that has the same purchasing power parity that the U.S. dollar had in the United States at a given point in time. It is widely used in economics. The years 1990 or 2000 are often used as a benchmark year for comparisons that run through time. The unit is often abbreviated e.g. 2000 US dollar (if the benchmark year is 2000) or 2000 Int$.
It is based on the twin concepts of purchasing power parities (PPP) of currencies and the international average prices of commodities. It shows how much a local currency unit is worth within the country's borders. It is used to make comparisons both between countries and over time. For example, comparing per capita gross domestic product (GDP) of various countries in international dollars, rather than based simply on exchange rates, provides a more valid measure to compare standards of living. It was proposed by Roy C. Geary in 1958 and developed by Salem Hanna Khamis between 1970 and 1972.
Figures expressed in international dollars cannot be converted to another country's currency using current market exchange rates; instead they must be converted using the country's PPP exchange rate used in the study.


由购买力平价学说(theory of Purchasing power parity简称PPP)和国际商品均价理论发展而来。 它体现一种货币的单位在国内价值是多少。把国际美元作为计价单位可以在不同国家和时期之间作较为准确的比较。例如在比较众多国家的人均GDP时，如果不通过简单的汇率计算转换成美元来比较，而是按国际美元计算的话，就会得出一个可以更加真实地体现不同国家生活水平的结果。



国际美元
也叫Geary-Khamis美元，一种在美国和给定时间点同美元具有同等购买力的假定货币。通常把1990年作为用于今后比较的基准年。
国际美元这一概念由Roy C. Geary在1958年提出。Salem Hanna Khamis在之前的基础上于1970到1972年间进行了发展和深化。
虽然这一术语不被广泛应用，但在一些国际组织机构如世界银行和国家货币基金组织出版的统计资料中时常会被用到。
研究中，在数字上，采用国际美元为单位的一国货币不能用当前市场汇率来转换为另一国家的货币，而应该先利用购买力平价系数调整系数转换为该国货币再通过市场汇率转换到另一个货币。