Perspectives on PPP and Long-Run Real Exchange Rates

This paper reviews the large and growing literature which tests PPP and other models of the long-run real exchange rate. We distinguish three different stages of PPP testing and focus on what has been learned from each. The most important overall lesson has been that the real exchange rate appears stationary over sufficiently long horizons. Simple, univariate random walk specifications can be rejected in favor of stationary alternatives. However, we argue that multivariate tests, which ask whether any linear combination of prices and exchange rates are stationary, have not necessarily provided meaningful rejections of nonstationarity. We also review a number of other theories of the long run real exchange rate -- including the Balassa-Samuelson hypothesis -- as well as the evidence supporting them. We argue that the persistence of real exchange rate movements can be generated by a number of sensible models and that Balassa- Samuelson effects seem important, but mainly for countries with widely disparate levels of income of growth. Finally, this paper presents new evidence testing the law of one price on 200 years of historical commodity price data for England and France, and uses a century of data from Argentina to test the possibility of sample-selection bias in tests of long-run PPP.