Comprehensive Notes on Exchange Rate Systems and Their Macroeconomic Impacts

Definition and Conceptual Framework of Exchange Rates

The exchange rate is fundamentally defined as the rate at which one currency trades for another within the foreign exchange (forex) market. This market is conceptually similar to any other commodity market where buyers and sellers trade goods; in this instance, the "goods" being exchanged are national currencies. The exchange rate is often described as the external value of a country’s currency. For instance, if the Singapore exchange rate is cited, it represents the specific quantity of foreign currency that can be obtained in exchange for one unit of Singapore's domestic currency. While it can also be expressed as the amount of domestic currency required to purchase one unit of foreign currency, the convention used here is the price of domestic currency in terms of foreign currency.

To provide a concrete example, if one Singapore Dollar ($S\$1.00$) exchanges for eighty cents of United States currency ($US\$0.80$), or sixty cents of Euro currency (\text{\euro}0.60), then the price of one Singapore Dollar is exactly that amount of foreign currency. The mathematical representation for this is expressed as $\text{Exchange rate} = \frac{x \text{ units of foreign currency}}{\text{one unit of domestic currency}}$. This formula reads as "$x$ units of foreign currency per unit of domestic currency," signifying the exchange value required to purchase a single unit of the domestic monetary unit. For the Singapore dollar example, the exchange rate would be written as \text{Exchange rate of S\} = \frac{US\0.80}{S\$1.00}.

The Foreign Exchange (Forex) Market and Rate Determination

Because the exchange rate is a price, it is determined by the intersection of demand and supply within the foreign exchange market. The forex market serves as the global marketplace where currencies are traded. While it can be visualized as a physical space "in between" nations where residents go to swap currencies, it is in reality a sophisticated electronic marketplace. For example, if a resident of the United States wishes to purchase Singaporean products, they must sell United States Dollars ($USD$) to buy Singapore Dollars ($SGD$). Conversely, a Singaporean resident wishing to buy American products must sell $SGD$ to acquire $USD$. In this scenario, the demand for $SGD$ originates from U.S. residents, while the supply of $SGD$ originates from Singapore residents.

The specific method by which a country’s exchange rate is determined depends heavily on the level of intervention by that country's Central Bank. Central Banks can intervene in the forex market much like a government might intervene in a commodity market. These various degrees of intervention categorize exchange rates into three distinct systems: the Floating (or Flexible) Exchange Rate System, the Fixed (or Pegged) Exchange Rate System, and the Managed Float (or Dirty Float) Exchange Rate System.

The Floating (or Flexible) Exchange Rate System

Under a floating exchange rate system, the Central Bank adopts a completely hands-off approach and does not intervene in the foreign exchange market. Consequently, the exchange rate is determined entirely by the competitive market forces of demand and supply. The demand for the domestic currency (for example, the S\) is generated by foreigners who require the currency to purchase domestic exports of goods and services or to acquire local financial and physical assets. The demand curve for the currency is downward-sloping, illustrating that at a lower exchange rate, domestic exports and assets become cheaper for foreigners, leading to a greater quantity of the domestic currency being demanded.

The supply of the domestic currency in a floating system comes from domestic residents who need to exchange their local money for foreign currency to purchase imports or acquire foreign assets. The supply curve is upward-sloping, indicating that as the exchange rate increases (meaning the domestic currency strengthens), foreign goods and assets become cheaper for locals, incentivizing them to sell a greater quantity of domestic currency to obtain the foreign currency necessary for those purchases. The equilibrium exchange rate is found where the demand and supply curves intersect ($D_{S\$} = S_{S\$}$). If the rate rises above equilibrium, a surplus of the currency occurs, exerting downward pressure. If the rate falls below equilibrium, a shortage occurs, exerting upward pressure until equilibrium is restored.

Factors Affecting Demand and Supply in Currency Markets

Several specific economic variables influence the demand for a currency. Firstly, interest rates play a significant role: higher relative domestic interest rates attract foreign investors seeking better returns, shifting the demand curve to the right, whereas lower interest rates shift it to the left. Secondly, inflation rates affect demand; low inflation maintains the currency's purchasing power, increasing its attractiveness, while high inflation reduces demand. Thirdly, foreign direct investment (FDI) inflows, driven by economic stability, political security, and investment-friendly policies, increase currency demand. Fourthly, an increase in export demand directly raises currency demand because buyers need the currency to pay for their imports. Finally, speculation influences the market; if traders anticipate a currency value will rise, they will purchase it, increasing current demand.

On the supply side, inflation rates also act as a driver; high domestic inflation makes foreign imports relatively cheaper, prompting locals to supply more domestic currency to pay for them. Interest rates in foreign countries also matter; if foreign rates are higher, locals may supply domestic currency to invest abroad in search of better returns (capital outflows). The total volume of imports is a direct factor, as higher imports require higher supply of the domestic currency to facilitate exchange. Capital outflows, caused by unfavorable domestic investment climates, similarly increase supply. Speculative behavior also impacts supply; if traders expect a currency to weaken in the future, they will sell off their holdings, effectively increasing the current supply on the market.

Currency Fluctuations: Appreciation and Depreciation

In the context of a floating exchange rate system, changes in market equilibrium are described using the terms appreciation and depreciation. Appreciation occurs when the external value of a currency rises, meaning one unit of domestic currency can now buy a greater amount of foreign currency. This happens under five conditions: an increase in demand, a fall in supply, demand increasing while supply falls, demand increasing more than supply increases, or supply falling more than demand falls. Graphically, an increase in demand from $D_1$ to $D_2$ creates a shortage ($Q_1Q_3$) at the original rate, pushing the price from $P_{S\$1}$ up to $P_{S\$2}$.

Depreciation is the opposite process, where the external value of a currency falls, meaning one unit of domestic currency buys less foreign currency. The currency is said to "weaken." This occurs when demand falls, supply increases, demand falls while supply increases, demand falls more than supply falls, or supply increases more than demand increases. For example, a shift from $D_1$ to $D_2$ (leftward) results in a surplus at the initial exchange rate, causing downward pressure and shifting the rate from $P_{S\$1}$ down to $P_{S\$2}$. Generally, large developed economies such as the United States, the United Kingdom, Japan, and the European Union utilize floating exchange rate systems.

The Fixed (or Pegged) Exchange Rate System

In a fixed exchange rate system, the Central Bank actively intervenes to maintain the currency at a specific, predetermined external value. To maintain this "peg," the Central Bank must be prepared to buy or sell its own currency in response to market shifts. If the market supply of the domestic currency increases (shifting the supply curve right from $SS_{S\$}$ to $SS'_{S\$}$), a surplus of the local currency is created. In a floating system, this would cause the rate to drop (e.g., from $S\$1 = US\$0.60$ to $S\$1 = US\$0.40$). To prevent this, the Central Bank utilizes its foreign exchange reserves to buy the surplus of domestic currency.

By purchasing the surplus, the Central Bank effectively increases market demand (shifting the demand curve from $DD_{S\$}$ to $DD'_{S\$}$), which offsets the increased supply and keeps the rate at the fixed level (e.g., $S\$1 = US\$0.60$). This intervention results in a decrease in the Central Bank's holdings of foreign reserves. If the situation were reversed (e.g., higher demand due to high exports), the Central Bank would sell domestic currency to meet the demand and maintain the peg, thereby increasing its foreign reserves. In fixed systems, if a Central Bank unilaterally decides to lower the fixed rate, it is called a devaluation; raising it is called a revaluation. This system is often used by developing nations to provide certainty and attract foreign direct investment (FDI) by ensuring asset values do not erode due to volatility.

The Managed Float (or Dirty Float) Exchange Rate System

The managed float system is a hybrid approach combining elements of both floating and fixed systems. Under this mechanism, the exchange rate is determined by market forces, but within a specific range established by the Central Bank known as an exchange rate band. This band consists of an upper limit ($ER_U$) and a lower limit ($ER_L$). If the exchange rate fluctuates within these bounds, the Central Bank allows market forces to operate without intervention. However, if market demand or supply shifts are significant enough to push the rate above the upper band or below the lower band, the Central Bank intervenes to pull it back into the target range.

Singapore is a prime example of a country that utilizes the managed float exchange rate system. The Monetary Authority of Singapore (MAS) is the central authority responsible for setting the band and conducting interventions. Rather than pegging to a single currency, Singapore uses a trade-weighted exchange rate, which measures the Singapore Dollar against a "basket" of currencies from its major trading partners. This trade-weighted index is reviewed semi-annually. This system provides stability by smoothing out short-term fluctuations while offering the flexibility to adjust to broader economic trends.

Mathematics of the Trade-Weighted Exchange Rate

A trade-weighted exchange rate calculates an average value based on the relative importance of different trading partners. For example, consider a scenario with three currencies: $1 \text{ Euro} = 1.5 \text{ SGD}$, $1 \text{ USD} = 1.4 \text{ SGD}$, and $1 \text{ Ringgit} = 0.3 \text{ SGD}$. If trade is distributed as $50\%$ with Malaysia, $20\%$ with the US, and $30\%$ with the EU, a representative "basket" would contain $5 \text{ Ringgit}$, $2 \text{ USD}$, and $3 \text{ Euros}$. The exchange rate of the basket is calculated as: $(5 \times 0.3) + (2 \times 1.4) + (3 \times 1.5) = 8.8 \text{ SGD}$.

If the individual rates change—for instance, if the Euro rises to $1.6 \text{ SGD}$, the USD falls to $1.0 \text{ SGD}$, and the Ringgit rises to $0.4 \text{ SGD}$—the new basket value would be $(5 \times 0.4) + (2 \times 1.0) + (3 \times 1.6) = 8.8 \text{ SGD}$. Despite the fluctuations in individual bilateral exchange rates, the overall trade-weighted exchange rate remains stable at $8.8 \text{ SGD}$. This stability is the reason MAS prefers this system, as it provides a mechanism to accommodate market noise while maintaining general currency strength relative to the nations Singapore trades with most.

Effects of Currency Appreciation on Net Exports (X-M)

Changes in the exchange rate directly impact net exports, which are calculated as $\text{Net Exports (X-M)} = \text{Export Revenue (X)} - \text{Import Expenditure (M)}$. Specifically, $\text{Export Revenue (X)} = (P_x \times Q_x)$ and $\text{Import Expenditure (M)} = (P_m \times Q_m)$. When a currency appreciates, domestic exports become more expensive in terms of foreign currency; foreigners find that they must pay more of their own currency to acquire the same domestic good. Meanwhile, imports become cheaper in terms of the domestic currency. Consequently, the quantity of exports demanded ($Q_x$) decreases, and the quantity of imports demanded ($Q_m$) increases as consumers switch from domestic products to the now-cheaper foreign alternatives.

Regarding export revenue ($X$) calculated in domestic currency: although the foreign price is higher, the domestic price ($P_x$) remains constant. Since the quantity ($Q_x$) has fallen, export revenue ($X$) will definitely decrease. Regarding import expenditure ($M$) in domestic currency: the domestic price ($P_m$) has fallen but the quantity ($Q_m$) has risen. The total expenditure depends on the Price Elasticity of Demand for imports ($|PED_m|$). If imports are price-elastic ($|PED_m| > 1$), the increase in $Q_m$ outweighs the fall in $P_m$, causing expenditure to rise. If imports are price-inelastic ($|PED_m| < 1$), the fall in $P_m$ outweighs the increase in $Q_m$, causing expenditure to fall.

The Marshall-Lerner Condition and Macroeconomic Impact

To determine the overall effect of an appreciation on net exports, economists use the Marshall-Lerner Condition. It states that an appreciation will lead to a decrease in net exports ($X-M$) provided that the sum of the price elasticities of demand for exports and imports is greater than one: $|PED_x + PED_m| > 1$. If this condition is met, an appreciation leads to a worsening of the Balance of Trade (BOT) and a fall in Net Exports. Conversely, a depreciation, assuming the Marshall-Lerner condition holds, would lead to an increase in Net Exports.

The resulting change in net exports ($X-M$) has significant implications for the broader economy. A fall in net exports (as caused by appreciation) leads to a decrease in Aggregate Demand ($AD$). Based on basic macroeconomic principles, a reduction in $AD$ will subsequently lead to a reduction in National Income ($NY$) and a decrease in the General Price Level ($GPL$). Conversely, a depreciation that increases net exports will raise $AD$, stimulating growth in $NY$ and potentially increasing the $GPL$. Therefore, exchange rate policy is a critical tool for managing a nation's internal economic stability and international competitiveness.