Temporal aggregation and purchasing power parity persistence

This paper uses a unique new monthly US–UK real exchange rate series for the January 1794–December 2009 period to reexamine the academic debate over purchasing power parity (PPP). The consensus view described by Rogoff (1996) is that PPP holds in the long-run, but short-run deviations are very persistent, with half-lives ranging from 3 to 5 years. Most of the literature using long time series relies on the annual data developed by Lee (1976) and Lothian and Taylor (1996), which were both constructed from underlying higher-frequency data sources. Estimates of purchasing power parity persistence using these series may therefore be subject to temporal aggregation bias. We find evidence of aggregation bias which indicates the half-life of PPP deviations has been overestimated in much of the previous literature. We also find that estimates of the half-lives are further reduced once we account for the Harrod (1933)–Balassa (1964)–Samuelson (1964) effect. The result of aggregation bias appears to be robust even when considering the case that real exchange rates exhibit nonlinear dynamics.

► We study the persistence of real exchange rate movements using 216 years of monthly data.
► Studies using annual data have overstated the persistence of PPP deviations due to aggregation bias.
► Accounting for nonlinearities and the Harrod–Balassa–Samuelson effect reduces persistence.
► Aggregation bias remains relevant after incorporating nonlinearities and the HBS effect.