Monday, December 24, 2007

PPP in Cointegrated Panels

A recent paper from the Fund;

Testing for Purchasing Power Parity in Cointegrated Panels
Summary: This paper applies the maximum likelihood panel cointegration method of Larsson and Lyhagen (2007) to test the strong PPP hypothesis using data for the G7 countries. This method is robust in several important dimensions relative to previous methods, including the well-known issue of cross-sectional dependence of error terms. The findings using this new method are contrasted to those from the Pedroni (1995) cointegration tests and fully modified OLS and dynamic OLS esimators of the cointegrating vectors. Our overall results are the same across all approaches: The strong PPP hypothesis is rejected in favour of weak PPP with heterogenenous cointegrating vectors.

Testing for PPP: Should we use panel methods?
Abstract. A common finding in the empirical literature on the validity of purchasing power parity (PPP) is that it holds when tested for in panel data, but not in univariate (i.e. country-specific) analysis. The usual explanation for this mismatch is that panel tests for unit roots are more powerful than their univariate counterparts. In this paper we suggest an alternative explanation. Existing panel methods assume that cross-unit cointegrating relationships, that would tie the units of the panel together, are not present. Using simulations, we show that if this important underlying assumption of panel unit root tests is violated, the empirical size of the tests is substantially higher than the nominal level, and the null hypothesis of a unit root is rejected too often even when it is true. More generally, this finding warns against the ‘‘automatic’’ use of panel methods for testing for unit roots in macroeconomic time series.

A Panic Attack on Unit Roots and Cointegration

The Purchasing Power Parity Puzzle, Kenneth Rogoff

An iTunes Index for Exchange Rates

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