Friday, September 05, 2008

Exchange rate forecasing

Jian Wang at Voxeu looks at the asset-price approach to exchange rate forecasting. This essentially says that exchange rates are based on forecasts of future fundamentals. Present fundamentals have a minor role. Future fundamentals are unknown. Therefore, they may not be any use in forecasting, but they would allow for some relationship between fundamentals and exchange rates.

This can also be related to the idea that portfolio flows respond to future fundamentals.

Engel and West (2005) argue that the exchange rate disconnect is consistent with exchange rates being determined by fundamental variables. They show that existing exchange rate models can be written in a present-value asset-pricing format. In these models, exchange rates are determined not only by current fundamentals but also by expectations of what the fundamentals will be in the future. Current fundamentals receive very little weight in determining the exchange rate. Not surprisingly, they aren’t useful in forecasting.

Under the Engel-West explanation, judging exchange rate models by their ability to forecast is too harsh a standard: If exchange rates are determined by fundamentals in the same way as other asset prices, current fundamentals can’t forecast exchange rates better than a random walk, even if the asset-pricing model correctly captures the relation between economic fundamentals and exchange rates. In this case, fundamental-based models are still appropriate for economic analysis, such as exchange rate and trade policy analysis – they are just useless in forecasting.

How do we know the asset-pricing model is applicable? Are there other ways to test fundamental-based exchange rate models if beating the random walk in forecasting exchange rates is too harsh? While the asset-pricing approach doesn’t allow us to predict short-term exchange rates, it does lead to an interesting implication. If the exchange rate is determined by expected future fundamentals, today’s currency values should contain information about tomorrow’s fundamentals.

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