Question

a) In the Dombusch model, the uncovered interest parity condition is assumed to hold continuously. If the domestic interest rate is lower than the foreign interest rate, then there is a need for an equivalent expected rate of appreciation of the domestic currency to compensate for the lower domestic interest rale. However, good prices adjust slowly over time to changes in the economy partly because wages are only adjusted periodically and partly because firms are also slow to adjust their prices upwards or downwards, due to 'sticky' domestic price.' Explain this statement using appropriate diagrams.( 20 marks)

b) Use the Dombusch model to explain an unexpected expansion of the money supply by 20% on economy ( 20 marks)

Answer 1

Dornbusch’s model makes the following assumptions: Uncovered interest-rate parity (UIP) states that the interest rate differential is equal to the expected change in the spot rate:

i_t − i_t^∗ = E_t Δs _{t +1}, where it and it*are the domestic and foreign interest rates at time t respectively and Et[Δst+1] is the expected change in the logarithm of the exchange rate1 . The model assumes that UIP holds at all times.

                                                         Figure 1

UIP assumes that capital is perfectly mobile, investors are risk neutral and domestic and foreign assets are perfect substitutes. The model assumes that the capital market adjusts instantaneously to shocks and that investors have rational expectations (Arnold, 2009). Absolute purchasing power parity (PPP) states that a basket of goods, when expressed in a common currency, should have the same cost across countries. PPP states that the real exchange rate, defined by Q_t = S_t P_t^* /P_t is equal to unity, where St is the spot rate and P_t and P_t^* are the domestic and foreign price levels respectively at time t. Setting Qt = 1 gives: P_t = SP_t^* . The price levels, expressed in a common currency, are equal (Pilbeam, 2006). The model assumes that deviations from PPP are permitted in the short run, but the exchange rate will return to PPP in the long run (Arnold, 2009). In the short run, the real exchange rate can rise which increases the competitiveness of the economy and increases net exports (Frankel, 1979). The assumption of long-run PPP is made because prices are ‘sticky’ in the short run due to nominal and real rigidities as in Keynesian theory (Romer, 2006).

A main feature of the model is that it allows a distinction between sluggishly-adjusting goods markets and hyperactive asset markets (Rogoff, 2002). The money market is in equilibrium when real money supply equals real money demand where real money demand is a rising function of output and a falling function of the interest rate: M_s^t /P_t = L(Y_t, i_t) (Arnold, 2009). Output is given by the standard IS curve, which is rising in the real exchange rate and falling in the interest rate (Copeland, 2008).

The inflation rate is a function of the output gap, given by the Phillips curve: ΔP_t+1 = ψ(y_t - ybar) where ∆p_t+1 is the change in the logarithm of the price level, y_t and ybar are the logarithms of output and potential output respectively and ψ is a measure of the price flexibility in the economy (Copeland, 2008). The economy under scrutiny is a small open economy so that it cannot affect foreign interest rates, prices and output.

The economy begins at a stationary state where: (i) output is at potential, (ii) PPP holds, (iii) domestic and foreign interest rates are equal, (iv) prices are constant, and (v) the exchange rate is at its equilibrium level. The stationary state, (Sbar, Pbar) is shown by point A in the Figure 1 below. Figure 1 (Dornbusch, 1976) The 45° line represents equilibrium PPP. Below the line, the economy is more competitive and net exports will rise. Above the line, the opposite is true. The ∆p_t+1 =0 line is the goods market when output is at potential. Below the line output is above potential and there is an upward pressure on prices (Pilbeam, 2006). The QQ schedule combines money market equilibrium and UIP.

At point A, the money market is clear, UIP holds and the domestic and foreign interest rates are equal. As the money market clears instantly and UIP holds at all times, the economy must be on the QQ schedule at all times.

Point A is the model’s stationary state (Dornbusch, 1976). The model analyses the dynamics of the economy after an unanticipated rise in the money supply. It is convenient to first analyse what will happen in the long run after the change in money supply before studying the short-run dynamics.

Solution to part (a) is shown in Figure 3.

b) The Long Run

By the quantity theory of money, a 20% rise in the money supply leads to a 20% rise in the price level. All else constant, a 20% rise in the price level must be matched by a 20% depreciation in the exchange rate to maintain PPP. This is as in the monetary model (Rosenberg, 1996). The rise in the money supply is given by a shift of the QQ schedule to Q’Q’. The new stationary state, is given by point C in Figure 2.

                                                         Figure 2

The Short Run

After the increase in money supply, the money market is in disequilibrium. The interest rate falls by the liquidity effect to increase money demand.

As i_t < i_t* (domestic interest rate is lower than foreign interest rate)foreign assets have become more attractive to investors. By UIP, individuals will only invest in domestic assets if they expect an appreciation in the exchange rate. But in the long run, as shown above, the exchange rate must depreciate overall. The exchange rate must therefore depreciate so much after the shock that it ‘overshoots’ its long-run equilibrium level and appreciate thereafter. The exchange rate jumps to point B in Figure 3. Figure 3 (Dornbusch, 1976) Because of a rise in the real exchange rate and a fall in the interest rate, output is above potential. By the Phillip’s curve, this gives an upward pressure on prices. The gradual appreciation of the exchange rate and inflation will lower the economy’s competitiveness until it reaches the new stationary state C in Figure 3.

Also, the fall in real money balances (due to the rising price level) will raise the interest rate back to its original level of i_t = i_t^* so there are no more expected changes in the exchange rate (Copeland, 2008; Dornbusch, 1976).

The time paths of the money supply, the exchange rate, the price level and the domestic interest rate are shown below in Figure 4.

The extent of the overshoot depends on the interest-sensitivity of the demand for money and how sensitive the market is about over-valuations and under-valuations of the currency (Dornbusch, 1976; Copeland 2008). Wilson (1979) analyses the case where the money supply shock is anticipated, rather than unanticipated in Dornbusch (1976). He demonstrates that the announcement or expectation of an expansionary policy alone will cause the exchange rate to jump – even before the policy is implemented.