内容提要： 马歇尔-勒纳条件是探讨货币贬值改善贸易收支的规律，本文根据人民币实际有效汇率的特点，把它分解为美元有效汇率和人民币对美元汇率之积形式，在此基础之上，本文重新考察货币贬值改善贸易收支的条件，对传统的马歇尔-勒纳条件进行修正。从我们研究中可以看出美元实际有效汇率变化对马歇尔-勒纳条件修正的重要作用，这包括美元有效汇率对人民币汇率弹性和人民币在美元有效汇率中的权重的两种影响。另一方面，即使人民币实际有效汇率贬值存在“J”曲线效应，人民币对美元实际汇率贬值，“J”曲线是否存在还要依赖一定的条件。本文实证研究结果显示出口（或进口）与人民币对美元实际汇率、美元实际有效汇率指数和外国收入（或国内收入）之间存在着显著的协整关系，美元实际有效汇率和人民币对美元实际汇率也存在显著的协整关系。从弹性的变化来看，修正的马歇尔-勒纳条件成立，同时人民币对美元实际汇率贬值有利于改善贸易收支，美元实际有效汇率贬值会恶化中国贸易收支。而对“J”曲线效应的实证研究显示无论是人民币实际有效汇率，还是人民币对美元实际汇率贬值和美元实际有效汇率贬值，我国“J”曲线效应均不显著。

关键词：实际有效汇率   贸易收支  需求弹性  马歇尔-勒纳条件  “J”曲线

The decomposition of RMB real effective exchange rate and the Marshall-Lerner condition revisions——An empirical analysis based on 1994-2011 data

Abstract: The Marshall-Lerner condition is the law of the currency devaluation to improve trade balance, according to the characteristics of RMB real effective exchange rate, this paper decomposes it into the product of US dollar effective exchange rates and RMB exchange rate against the dollar, on this basis, this paper re-examine the traditional Marshall-Lerner condition of currency devaluation to improve the trade balance. From our studies, it can be seen that US dollar real effective exchange rate plays an important role in revising the Marshall-Lerner condition, such as the effects of US dollar real effective exchange rate elasticity against RMB exchange rate and the Yuan's weight in the US dollar effective exchange rate index. On the other hand, even though "J" curve effect holds under the depreciation of RMB real effective exchange rate, whether "J" curve exists or not depends on some certain condition under RMB real exchange rate depreciation against the US dollar. This empirical results reveals among exports (or imports), Yuan real exchange rate against US dollar, US dollar real effective exchange rate index and foreign income (or domestic income) ,there exists an significant cointegration relationship, and between US Dollar real effective exchange rate and Yuan real exchange rate against US Dollar, there also exists a significant cointegration relationship. From the elasticity changes, the revised Marshall-Lerner conditions hold, meanwhile the devaluation of RMB real exchange rate against the dollar can improve the trade balance and the devaluation of US dollar real effective exchange rate may have the negative effects. The empirical studies on "J" curve show no matter whether RMB real effective exchange rate or RMB real exchange rate against the US dollar and US dollar real effective exchange rate are depreciated, J" curve effect is not significant.

Key words: real effective exchange rate   trade balance   demand elasticity   Marshall-Lerner condition   “J” curve

最早的经常帐户和汇率的模型是弹性的分析方法，弹性分析方法来源于两方面的理论贡献：一是外汇市场供给和需求理论的发展；二是探讨外汇市场稳定的标准，即外汇市场的均衡。在此基础上，毕克戴克、鲁宾逊和梅茨勒（Bickerdike,Joan，1920;Robinson,Brown,1947;Metzler，1948）研究了汇率稳定（国际收支均衡）的标准，这就是所谓的毕克戴克－鲁宾逊－梅茨勒（Bickerdike－Robinson－Metzler）条件，它是在马歇尔(Marshall)微观经济学的基础上建立起来的。1944年勒纳（Abba Lerner）给出了贬值改善贸易收支的的临界条件－马歇尔－勒纳条件[1]（Mashall－Lerner condition），即出口和进口的需求弹性之和大于1，则货币贬值将有利于改善贸易收支。短期内货币贬值可能会恶化贸易收支，长期内改善贸易收支，存在“J”曲线效应。弹性方法主要是从商品市场的角度分析汇率贬值导致相对价格的改变而影响经常帐户的均衡，Dornbusch and Krugman(1976)认为货币贬值对贸易收支有短暂的负的影响，但如果出口汇率弹性较大，长期来看，货币贬值将改善贸易收支。货币贬值其结果是在马歇尔－勒纳条件存在的情况下，出口的增长率上升，进口的增长率削减，贸易收支改善，货币贬值的数量效应超过了价格效应。如果两国的一般价格水平不变，名义汇率的变动就导致实际汇率的变动，贬值提高了国内产品的竞争力。