Getting PPP right: Identifying mean-reverting real exchange rates in panels

Recent advances in testing for the validity of Purchasing Power Parity (PPP) focus on the time series properties of real exchange rates in panel frameworks. One weakness of such tests, however, is that they fail to inform the researcher as to which cross-section units are stationary. As a consequence, a reservation for PPP analyses based on such tests is that a small number of real exchange rates in a given panel may drive the results. In this paper we examine the PPP hypothesis focusing on the stationarity of the real exchange rates in up to 25 OECD countries. We introduce a methodology that when applied to a set of established panel unit-root tests, allows the identification of the real exchange rates that are stationary. Our results reveal evidence of mean-reversion that is significantly stronger as compared to that obtained by the existing literature, strengthening the case for PPP.     

The behaviour of the real exchange rate: Evidence from regression quantiles

We test for mean reversion in real exchange rates using a recently developed unit root test for non-normal processes based on quantile autoregression inference in semi-parametric and non-parametric settings. The quantile regression approach allows us to directly capture the impact of different magnitudes of shocks that hit the real exchange rate, conditional on its past history, and can detect asymmetric, dynamic adjustment of the real exchange rate towards its long run equilibrium. It, therefore provides a detailed mapping of the real exchange rate behaviour, while being a robust alternative to previous unit root tests. The latter is confirmed by a simulation analysis comparing the power of the alternative tests. As concerns the real exchange rate, our results suggest that large shocks tend to induce strong mean reverting tendencies in the exchange rate, with half lives less than one year in the extreme quantiles. Mean reversion is faster when large shocks originate at points of large real exchange rate deviations from the long run equilibrium. However, in the absence of shocks no mean reversion is observed. Finally, we report asymmetries in the dynamic adjustment of the RER.     

Local persistence and the PPP hypothesis

This paper examines the statistical properties of the bilateral real exchange rates of the U.S. vs. France, Germany, and the U.K. during the Post-Bretton-Woods period, and draws implications on the Purchasing Power Parity (PPP) hypothesis. Contrary to traditional studies that consider only unit root and stationary processes to describe the real exchange rate behavior, this paper considers an in-between process, the locally persistent process. The empirical results demonstrate the following two findings: (1) Locally persistent processes describe the real exchange rate movements better than unit root and stationary processes, which implies that PPP reversion occurs and PPP holds in the long-run. (2) The confidence intervals for half-life deviations from PPP under local persistence tend to be narrower than those obtained by assuming the ADF and the local-to-unity models.     

购买力平价理论的实证检验法综述

本文介绍了自 2 0世纪 70年代以来开放经济理论的基石———购买力平价及实际汇率的相关实证检验方法。以发达国家双边汇率作为样本数据进行检验 ,发现在样本期间足够长、样本数量足够多的情况下 ,PPP假设成立。此外 ,由于实际汇率对PPP的均值复归呈现出显著的非线性特征 ,今后的研究方向应当是建立非线性汇率动态模型。     

Bivariate relative city price convergence in the United States: 1918-1997

As in international tests of purchasing power parity, panel unit root tests have been successful in rejecting a unit root process in U.S. city relative prices over the period 1918-1997. However, there is an empirical question of what the rejection of a ‘panel unit root’, particularly with respect to real exchange rates, means. This paper employs a variety of univariate unit root and cointegration tests which have recently come to the fore. These tests improve the power and reduce size distortion found in standard unit root and cointegration tests such as the Dickey-Fuller and Phillips-Perron tests. I find considerable evidence for rejecting a unit root process in the majority of U.S. city relative prices over the entire sample period and two subperiods. Less successful are stationarity tests conducted on regions of the U.S.     

A century of purchasing power parity confirmed: The role of nonlinearity

Taylor (2002) claims that Purchasing Power Parity (PPP) has held over the 20th century based on strong evidence of stationary for century-long real exchange rates for 20 countries. Lopez et al. (2005), however, found much weaker evidence of PPP with alternative lag selection methods. We reevaluate Taylor’s claim by implementing a recently developed nonlinear unit root test by Park and Shintani (2005). We find strong evidence of nonlinear mean-reversion in real exchange rates that confirms Taylor’s claim. We also find a possible misspecification problem in using the ESTAR model that may not be detected with Taylor-approximation based tests.     

Purchasing power parity in ASEAN-5 countries: revisit with cross-sectional dependence and structural breaks

This paper re-examines the purchasing power parity (PPP) hypothesis for a panel of ASEAN-5 countries. The panel unit root and cointegration tests, which incorporate cross-sectional dependence and multiple structural breaks, are innovatively used for testing the PPP hypothesis. We could not find evidence that supports the existence of a long-run equilibrium between the relative price ratio and the nominal exchange rate for the whole period. Nevertheless, there is evidence of a cointegrating relationship for the post-crisis period. Our finding implies that a flexible exchange rate regime is suitable for the individual ASEAN countries.     

Mean reversion in long-horizon real exchange rates: Evidence from Latin America

This paper examines mean reversion in real effective exchange rates in six leading Latin American economies during the XXth century using a new data set. A unit-root approach is complemented by an error-correction model including key fundamentals such as terms of trade, trade openness and relative productivities. Unit-root testing shows a very slow process of reversion – if any – to a constant mean in the original series, rejecting the strict PPP hypothesis; however, mean reversion is found after allowing for trends and structural breaks with a half-life average of 1½ years for the six countries. We also found reversion to a conditional mean defined by the co-integrating relationship with an average half-life of 2½ years. Our estimates, although lower than the 3–5 year range that motivated the Rogoff’s puzzle, still indicate the presence of important obstacles to the adjustment process that need further investigation.     

Cross‐sectional Restrictions on the Spot and Forward Term Structures of Interest Rates and Panel Unit Root Tests

In this paper we examine the stationarity of all the rates comprising the USD, GBP, DM and JPY spot and forward term structures. Instead of focussing on short maturity interest rates, as most other papers do, we perform a detailed analysis of the whole range of spot and forward interest rates of the 4 main currencies. We investigate the issue of stationarity within the framework of an equilibrium interest rate model such as Vasicek (1977), that defines the cross-sectional and time series properties that interest rates of various maturities must satisfy. We show that within a one-factor interest rate model, such as Vasicek, all interest rates are restricted to exhibit the same mean reverting behaviour. This restriction allows us to apply more powerful panel unit root tests. This methodology increases considerably the number of observations available and as a result the power of the unit root tests. The higher power of these tests allows us to demonstrate that there does exist mean reversion on the spot and forward US interest rates and the forward DM and GBP interest rates.     

Nonlinear exchange rate predictability

We study whether the nonlinear behavior of the real exchange rate can help us account for the lack of predictability of the nominal exchange rate. We construct a smooth nonlinear error-correction model that allows us to test the hypotheses of nonlinear predictability of the nominal exchange rate and nonlinear behavior on the real exchange rate in the context of a fully specified cointegrated system. Using a panel of 19 countries and three numeraires, we find evidence of nonlinear predictability of the nominal exchange rate and of nonlinear mean reversion of the real exchange rate. Out-of-sample Theil’s U -statistics show a higher forecast precision of the nonlinear model than the one obtained with a random walk specification. Although the robustness of the out-of-sample results over different forecast windows is somewhat limited, we are able to obtain significant predictability gains—from a parsimonious structural model with PPP fundamentals—even at short-run horizons.     

Exchange rate mean reversion from real shocks within an intertemporal equilibrium model

The post Bretton Woods era has been characterized by real exchange rates that exhibit mean reversion, with mixed evidence as to whether this reversion is partial (PPP never holds) or essentially complete. This paper generates these stylized facts theoretically by synthesizing a simple intertemporal open economy model with the elasticities approach to the current account. A central feature of the model is the existence of non-traded goods. The model can generate partial or approximately complete mean reversion for the real exchange rate (depending on parameter values) if innovations in output are made up of permanent and temporary components. In addition, temporary output shocks generate a type of hysteresis wherein the short-run path for the exchange rate permanently alters its long-run equilibrium value.     

Real exchange rate adjustment in European transition countries

In single-equation tests, real exchange rates show mean reversion for nine of 10 Central and Eastern European transition countries for the period January 1993 to December 2005. Because of the shift from controlled to market economies and accompanying crises, failed policy regimes and changes in exchange rate regimes, unit root tests for transition countries often require allowance for structural changes. Accounting for structural breaks gives substantially faster mean-reversion speeds than those found for major industrialized countries. These fast adjustment speeds are plausible: Transition countries had perhaps 10 years to make unprecedented adjustments required for accession to the European Union. A number of papers have applied non-linear models to the Central and Eastern European countries. This paper investigates four non-linear models and compares them with piece-wise linear break models. The break models appear superior in detecting mean reversion for the Central and Eastern European transition countries.     

Purchasing power parity: Modeling and testing mean reversion

A model of mean reversion of exchange rates to purchasing power parity is developed and tested where exchange rates are assumed to follow a mean reverting elastic random walk toward a stochastic PPP rate. The model recognizes the possibility that mean reversion towards PPP may be nonlinear which allows greater flexibility in the adjustment process. Regression equations consistent with the theoretical model are derived. The model is tested using long- and short-term data for six countries. While the results are generally consistent with the findings of previous studies, evidence is presented which demonstrates that the mean reversion process is not linear for some countries.     

Further on nonlinearity,persistence, and integration properties of real exchange rates

Integration, nonlinearity, and persistence dynamics of several quarterly US-Dollar-denominated real exchange rates are investigated by using new unit root tests, simulated p-values for linearity tests, estimation of smooth transition autoregressive (STAR) models, and simulation of autocorrelation functions. This paper uses a simulation-based approach to study covariance stationarity and persistence dynamics of the estimated models. Findings in the paper provide evidence of nonlinear mean reversion for several series albeit with some persistence. Results also reveal considerable variation in the degree of persistence and timing of switches across extreme regimes in ESTAR models between Euro and non-Euro area currencies.     

Purchasing power parity, unit roots, and dynamic structure

Recent studies of purchasing power parity (PPP) account for the possible presence of unit roots in nominal exchange rates and relative price indices by applying standard unit-root tests to real exchange rates, which are ratios of nominal exchange rates and relative price indices. These studies occasionally find evidence of PPP, but as a whole, the evidence is not definitive. Standard unit-root tests impose a restrictive dynamic structure between nominal exchange rates and relative price indices. I specify and estimate a generalized dynamic structure. I reject the dynamic restrictions implicit in standard unit-root tests of PPP, and find stronger evidence of PPP than do most other recent studies.     

Testing the Purchasing Power Parity Hypothesis for the New Member and Candidate Countries of the European Union: Evidence from Lagrange Multiplier Unit Root Tests with Structural Breaks

This paper investigates the validity of purchasing power parity (PPP) for the eleven Central and East European transition countries and three market economy countries, Cyprus, Malta, and Turkey. Unlike previous studies on PPP, this study uses Lagrange multiplier (LM) unit root tests that incorporate structural breaks in the data series. The findings indicate that in cases of one and two structural breaks, for a U.S. dollar-based real exchange rate series, there is little evidence supporting the validity of PPP. For a deutsche mark-based real exchange rate series, for the cases of both one and two breaks, there is evidence of stationarity of real exchange rates for eight sample countries, which is consistent with PPP. The results also indicate that the estimated half-life of a shock to the real exchange rate ranges from 1.25 (15.05 months) to 2.72 (32.72 months) years across countries. The empirical findings may provide direction for policy makers to coordinate monetary policies for the process of European monetary integration.     

Multivariate unit root tests of the PPP hypothesis

So far, most univariate tests of Purchasing Power Parity (PPP) have provided mixed support for PPP. In contrast, this paper focuses on a multivariate framework, which produces much stronger results. Unlike previous panel tests, however, we do not impose a common speed of mean reversion. The contribution of this paper is to show that the increased power of multivariate tests stems from high correlations across series, and not necessarily from imposing a common speed of mean reversion. We find strong evidence in favor of long-run PPP, which we show can be traced to the dollar vs. European currencies.     

How well does nonlinear mean reversion solve the PPP puzzle?

This paper addresses the degree to which models which exhibit nonlinear mean reversion (NMR) present a resolution to the Purchasing Power Parity Puzzle. This paper develops a method of estimating a representative distribution of half lives which is based upon the observed distribution of shocks in a given time series rather than choosing shock sizes arbitrarily which is the current practice in the literature. This approach is implemented with data on five real exchange rates. The empirical analysis shows that half lives shorter than the consensus are observed frequently enough to support the proposition that NMR is a solution to the PPP puzzle.     

Searching for evidence of long-run PPP from a post-Bretton Woods panel: separating the wheat from the chaff

This paper reexamines the issue of long-run PPP using multiple panel tests in the framework of confirmatory analysis. Application of six panel tests under competing null hypotheses to the real exchange rates of 21 industrial countries yields seemingly contradictory evidence on the parity during the post-Bretton Woods period. Regardless of numeraire currency, four I(1) panel tests unanimously reject the null hypothesis in favor of long-run PPP, whereas two I(0) panel tests lend little support to the parity at conventional significance levels. Confirmatory analysis suggests that this puzzling result can be explained either by nonlinear dynamics of the real exchange rates or by a mixture of I(0) and I(1) series in the panel. Monte Carlo experiments indicate that potential mix of I(0) and I(1) series is more relevant to the empirical finding. The use of a sequential classification method sorts out six real exchange rates which exhibit most persistent deviations from long-run equilibrium. Systematic behavior of these series can be characterized better by country specific factors than by observable macroeconomic variables.     

Smooth breaks and non-linear mean reversion: Post-Bretton Woods real exchange rates

The recent literature on Purchasing Power Parity (PPP) has emphasized the role of two phenomena that may lead to the rejection of the PPP hypothesis: structural breaks and non-linear adjustment induced by transaction costs. These two hypotheses are analyzed separately in the literature. We develop tests for unit roots that account jointly for structural breaks and non-linear adjustment. Structural breaks are modeled by means of a Fourier function that allows for infrequent smooth temporary mean changes and is hence compatible with long-run PPP. Nonlinear adjustment is modeled by means of an ESTAR model. Our tests present good finite sample properties. The tests are applied to a set of 15 OECD countries' RERs and are able to reject the null of a unit root in 14 cases. The breaks are usually associated with the great appreciation and later depreciation of the dollar in the 1980s and the ESTAR adjustment appears to play an important role.