The Unassuming Economist

From a new ECB working paper:

“The international finance literature has documented two important regularities in foreign exchange markets. First, there is ample evidence that, for developed countries, real exchange rates are reverting to the level implied by the Purchasing Power Parity (PPP) theory. Second, for flexible currency regimes the adjustment process is mainly driven by the nominal exchange rate. At the same time most of the recent articles remain skeptical that one can outperform the random walk (RW) in nominal exchange rate forecasting.

In this paper we claim that the two above in-sample regularities of foreign exchange markets can be exploited to infer out-of-sample movements of major currency pairs. To prove this thesis we proceed as follows:

1. We begin by presenting robust (in-sample) evidence that, for major currency pairs, long-run PPP holds and that the nominal exchange rate is the main driver of this adjustment process.
2. We then evaluate a battery of models that aim to exploit these in-sample regularities for forecasting purposes. The winner of the forecasting race is a calibrated PPP model, which just assumes that the real exchange rate gradually returns to its sample mean, completing half of the adjustment in 3 years, and that the adjustment is only driven by the nominal exchange rate. This approach is so simple that it can be implemented even on the back of a napkin in two steps. Step 1 consists in calculating the initial real exchange rate misalignment with an eyeball estimate of what is the distance from the sample mean. Step 2 consists in recalling that, according to this model, one tenth of the required adjustment is achieved by the nominal exchange rate in the first 6 months, one fifth in one year, just over a third in two years and exactly half after 3 years.
3. We highlight that severe problems arise when attempting to carry out more sophisticated approaches, such as estimating the pace of mean reversion of the real exchange rate or forecasting relative inflation. Among the estimated approaches, we find that it is strongly preferable to rely on direct rather than multi-step iterative forecasting methods. We also find that models estimated with panel data techniques perform only marginally better than those based on individual currency pairs. This finding has bittersweet implications. On the negative side, estimated models encounter a second formidable competitor that, like the RW, bypasses the estimation error problem. On the positive side, the HL model is more acceptable than the RW from the perspective of economic theory.
4. This analysis highlights also that equilibrium exchange rate analysis matters. Simple measures of exchange rate disequilibria, not only signal economic imbalances, but also provide hints in which direction the exchange rate will go.

Our paper has an important message for policymakers. For advanced countries, it is better to rely on the concept of long-run PPP rather than on the RW.”