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88 Krugman/Obstfeld/Melitz • International Economics: Theory & Policy, Ninth Edition
Chapter 17
Output and the Exchange Rate
in the Short Run
.1 Chapter Organization
Determinants of Aggregate Demand in an Open Economy
Determinants of Consumption Demand
Determinants of the Current Account
How Real Exchange Rate Changes Affect the Current Account
How Disposable Income Changes Affect the Current Account
The Equation of Aggregate Demand
The Real Exchange Rate and Aggregate Demand
Real Income and Aggregate Demand
How Output Is Determined in the Short Run
Output Market Equilibrium in the Short Run: The DD Schedule
Output, the Exchange Rate, and Output Market Equilibrium
Deriving the DD Schedule
Factors That Shift the DD Schedule
Asset Market Equilibrium in the Short Run: The AA Schedule
Output, the Exchange Rate, and Asset Market Equilibrium
Deriving the AA Schedule
Factors That Shift the AA Schedule
Short-Run Equilibrium for the Economy: Putting the DD and AA Schedules Together
Temporary Changes in Monetary and Fiscal Policy
Monetary Policy
Fiscal Policy
Policies to Maintain Full Employment
Inflation Bias and Other Problems of Policy Formulation
© 2012 Pearson Education, Inc. Publishing as Addison-Wesley
89 Krugman/Obstfeld/Melitz • International Economics: Theory & Policy, Ninth Edition
Permanent Shifts in Monetary and Fiscal Policy
A Permanent Increase in the Money Supply
Adjustment to a Permanent Increase in the Money Supply
A Permanent Fiscal ExpansionMacroeconomic Policies and the Current Account
Gradual Trade Adjustment and Current Account Dynamics
The J-Curve
Exchange Rate Pass-Through and Inflation
Box: Exchange Rates and the Current Account
The Liquidity Trap
Summary
APPENDIX 1 TO CHAPTER 17: Intertemporal Trade and Consumption Demand
APPENDIX 2 TO CHAPTER 17: The Marshall-Lerner Condition and Empirical Estimates
of Trade Elasticities
Online Appendix: The IS-LM and the DD-AA Model
.2 Chapter Overview
This chapter integrates the previous analysis of exchange rate determination with a model of short-run
output determination in an open economy. The model presented is similar in spirit to the classic
Mundell-Fleming model, but the discussion goes beyond the standard presentation in its contrast of the
effects of temporary versus permanent policies. The distinction between temporary and permanent policies
allows for an analysis of dynamic paths of adjustment rather than just comparative statics. This dynamic
analysis brings in the possibility of a J-curve response of the current account to currency depreciation. The
chapter concludes with a discussion of exchange rate pass-through, that is, the response of import prices to
exchange rate movements.
The chapter begins with the development of an open-economy fixed-price model. An aggregate demand
function is derived using a Keynesian cross diagram in which the real exchange rate serves as a shift
parameter. A nominal currency depreciation increases output by stimulating exports and reducing imports,
given foreign and domestic prices, fiscal policy, and investment levels. This yields a positively sloped
output-market equilibrium (DD) schedule in exchange rate output space. A negatively sloped asset-market
equilibrium (AA) schedule completes the model. The derivation of this schedule follows from the analysis
of previous chapters. For students who have already taken intermediate macroeconomics, you may want to
point out that the intuition behind the slope of the AA curve is identical to that of the LM curve, with the
additional relationship of interest parity providing the link between the closed-economy LM curve and the
open-economy AA curve. As with the LM curve, higher income increases money demand and raises the
home-currency interest rate (given real balances). In an open economy, higher interest rates require currency
appreciation to satisfy interest parity (for a given future expected exchange rate).
The effects of temporary policies as well as the short-run and long-run effects of permanent policies can be
studied in the context of the DD-AA model if we identify the expected future exchange rate with the
long-run exchange rate examined in Chapters 15 and 16. In line with this interpretation, temporary policies
are defined to be those which leave the expected exchange rate unchanged, while permanent policies are
those which move the expected exchange rate to its new long-run level. As in the analysis in earlier
chapters, in the long run, prices change to clear markets (if necessary). While the assumptions concerning the
expectational effects of temporary and permanent policies are unrealistic as an exact description of an
economy, they are pedagogically useful because they allow students to grasp how differing market
© 2012 Pearson Education, Inc. Publishing as Addison-Wesley
Chapter 17 Output and the Exchange Rate in the Short Run 90
expectations about the duration of policies can alter their qualitative effects. Students may find the
distinction between temporary and permanent, on the one hand, and between short run and long run, on the
other, a bit confusing at first. It is probably worthwhile to spend a few minutes discussing this topic.
Both temporary and permanent increases in money supply expand output in the short run through exchange
rate depreciation. The long-run analysis of a permanent monetary change once again shows how the
well-known Dornbusch overshooting result can occur. Temporary expansionary fiscal policy raises output
in the short run and causes the exchange rate to appreciate. Permanent fiscal expansion, however, has no
effect on output even in the short run. The reason for this is that, given the assumptions of the model, the
currency appreciation in response to permanent fiscal expansion completely “crowds out” exports. This is
a consequence of the effect of a permanent fiscal expansion on the expected long-run exchange rate which
shifts inward the asset-market equilibrium curve. This model can be used to explain the consequences of
U.S. fiscal and monetary policies between 1979 and 1984. The model explains the recession of 1982 and
the appreciation of the dollar as a result of tight monetary and loose fiscal policy.
The chapter concludes with some discussion of real-world modifications of the basic model. Recent
experience casts doubt on a tight, unvarying relationship between movements in the nominal exchange rate
and shifts in competitiveness and thus between nominal exchange rate movements and movements in the
trade balance as depicted in the DD-AA model. Exchange rate pass-through is less than complete and thus
nominal exchange rate movements are not translated one-for-one into changes in the real exchange rate.
Also, the current account may worsen immediately after currency depreciation. This J-curve effect occurs
because of time lags in deliveries and because of low elasticities of demand in the short run as compared to
the long run. The chapter contains a discussion of the way in which the analysis of the model would be
affected by the inclusion of incomplete exchange rate pass-through and time-varying elasticities. Appendix 2
provides further information on trade elasticities with a presentation of the Marshall-Lerner conditions and
a reporting of estimates of the impact of short-run and long-run elasticities of demand for international
trade in manufactured goods for a number of countries.
A discussion of how the current account balance can affect the exchange rate is also illuminating: a country
running a persistent current account deficit will experience a loss in net foreign wealth, which in turn may
depreciate the currency given home biases in consumption. This observation is matched with U.S. data to
illustrate that fiscal expansions in the United States that initially lead to currency appreciations and current
account deficits will, over time, lead to depreciations in the dollar. The chapter concludes with the efficacy
of monetary policy in a liquidity trap. When nominal interest rates are at zero (as they effectively were in
the United States in 2010), any attempt to stimulate the economy through monetary expansion will be
ineffective given that interest rates cannot fall below zero. A modification of the DD-AA model shows that
for a country in a liquidity trap, a section of the AA curve is perfectly elastic. In fact, monetary policy can
only affect output by changing the expected exchange rate. This may explain the unconventional monetary
policies recently taken by the Federal Reserve such as the purchase of long-term government bonds.
© 2012 Pearson Education, Inc. Publishing as Addison-Wesley
