## Reconciling Random Walks and Predictability: A Dual- Component Model of Exchange Rate Dynamics

_IMF Working Papers, December 13, 2024_

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## Bibliographic details
- Authors: Bas B. Bakker
- Published: December 13, 2024
- Series: IMF Working Papers
- DOI: https://doi.org/10.5089/9798400295034.001

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### Summary and research question
- Addresses whether exchange rates follow a random walk or exhibit predictable patterns.
- Demonstrates that exchange rates can possess a unit root while maintaining substantial predictability over certain horizons.
- Proposes a dual-component model combining:
  - A stochastic trend representing the slowly moving equilibrium exchange rate.
  - A stationary cyclical component capturing temporary deviations.

### Model structure and key mechanisms
- Dual-component framework reconciles long-term random walk behavior with medium-term predictability.
- Role of components:
  - Stochastic trend: slow-moving equilibrium exchange rate; imparts unit root behavior.
  - Stationary cyclical component: temporary deviations that generate nonzero expected changes and a strong level–change relationship.
- Without the stationary component, expected exchange rate changes would be zero.
- If the stochastic trend evolves too quickly, the relationship between level and expected future changes would break down.
- Extension: builds on Bacchetta and van Wincoop (2021) by adding a stochastic trend to generate both stationary and stochastic-trend behavior.

### Main theoretical predictions
- Expected exchange rate changes are not zero.
- Expected exchange rate changes are highly persistent.
- Strong relationship between exchange rate levels and expected future changes.
- Forecast accuracy follows an inverted U-shaped pattern: accuracy peaks at intermediate horizons.
- Multi-year exchange rate changes are increasing multiples of one-year changes.

### Empirical evidence and data
- Data: 2000–2024 for nine inflation-targeting countries with freely floating exchange rates.
- Empirical findings:
  - Strong empirical support for the model’s predictions.
  - The model consistently outperforms the random walk benchmark in out-of-sample tests.

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_Source: https://www.imf.org/en/publications/wp/issues/2024/12/14/reconciling-random-walks-and-predictability-a-dual-component-model-of-exchange-rate-dynamics-559469_