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Theories of Exchange Rate Determination
These theories attempt to explain how and why exchange rates fluctuate or remain stable over time. The major theories include:
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1. Purchasing Power Parity (PPP) Theory
Definition:
This theory states that the exchange rate between two currencies is determined by the relative purchasing power of those currencies in their respective countries.
Formula:
Exchange Rate = Price Level in Domestic Country / Price Level in Foreign Country
Example:
If a basket of goods costs ₹1000 in India and $10 in the USA, the exchange rate should be ₹1000/$10 = ₹100 per $1.
Assumptions:
No transportation costs
No trade restrictions (tariffs, quotas)
Identical goods in both countries
Limitations:
Not realistic in the short term due to market imperfections, inflation differences, and government policies.
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2. Interest Rate Parity (IRP) Theory
Definition:
This theory states that the difference in interest rates between two countries will be offset by the change in exchange rates.
Implication:
Investors should earn the same return in both countries after accounting for exchange rate changes, preventing arbitrage opportunities.
Formula:
(Forward Rate - Spot Rate) / Spot Rate = Interest Rate Differential
Use:
Helps in predicting forward exchange rates and guiding investment decisions in international finance.
Limitations:
Assumes perfect capital mobility
Ignores transaction costs and risks
Not always accurate in the real world
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3. Balance of Payments (BOP) Theory
Definition:
This theory states that the exchange rate is determined by a country's balance of payments position — the difference between its total exports and total imports (including services and capital flows).
Implication:
A surplus in BOP leads to currency appreciation.
A deficit in BOP leads to currency depreciation.
Focus:
Entire economic transactions (not just trade)
Includes capital flows, remittances, and reserves
Limitations:
Ignores the impact of speculation and government intervention
Assumes trade is the main driver, not capital flow (less realistic in modern economies)
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4. Asset Market Theory
Definition:
This theory considers exchange rates as determined by the supply and demand for financial assets (stocks, bonds, and currencies) rather than goods and services.
Focus:
Investor preferences, interest rates, risk, and expected returns on foreign assets.
Key Point:
Currencies are seen like assets — their value changes based on investors’ perception of profitability and safety.
Strength:
Explains short-term volatility in exchange rates better than PPP or BOP theory.
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5. Monetary Approach Theory
Definition:
This theory says exchange rates are determined by the relative supply and demand of money in two countries.
Implication:
If a country increases its money supply without a matching increase in output, its currency will depreciate.
A stable money supply supports a strong currency.
Assumptions:
Prices are flexible
Full employment exists
No capital controls
Limitations:
Overly theoretical
Less effective for short-term exchange rate prediction
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Conclusion
In practice, no single theory works perfectly, and a combination is often used to understand and predict exchange rate movements.
