The Mundell-Fleming model From IS-LM to Mundell-Fleming Policy in an open economy.
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The Mundell-Fleming model
From IS-LM to Mundell-FlemingPolicy in an open economy
The Mundell-Fleming model
Last week we introduced the basic elements required to analyse an open economyThe current account: imports and
exportsThe capital account: saving/investment
flowsThe balance of payments equilibrium as
a combination of the twoThe role of exchange rates
The Mundell-Fleming model
This week we integrate these elements into the Mundell-Fleming model, which is an IS-LM model extended to account for imports and exports Although this will not be covered, in theory this
can be used in turn to modify the AS-AD model to account for international trade with inflation
As we saw last week, the price level can be included through the analysis of real exchange rates
The Mundell-Fleming model
From IS-LM to the Mundell-Fleming model
Effectiveness of policy
From IS-LM to Mundell-Fleming
Model developed by Robert Mundell and Marcus Fleming It extends the IS-LM model to an open economy
Aggregate demand now contains the current account : i.e. the difference between exports and imports. X(Y*,e) : Exports are a function of the income of
the rest of the world (exogenous) and the exchange rate
M(Y,e) : Importations are a function of national income and the exchange rate
*, ,X YY C Y T I i G e M Y e
From IS-LM to Mundell-Fleming
Determinants of the current account: If e falls (depreciation): exportations are more
competitive and imports more expensive. The net balance of the current account increases.
If Y increases: imports increase and the net balance of the current account falls.
Y* is exogenous, and Y is already determined in IS-LM. There is an extra variable to account for: the exchange rate e.
We need to add another equation (market) in order to be able to solve the system: we use the equilibrium condition on the balance of payments
* *, , , ,CA Y Y e X Y e M Y e
The equilibrium exchange rate is achieved when BP is equal to zero, in other words when the deficits and surpluses of the two accounts compensate exactly.
From IS-LM to Mundell-Fleming
One can see that this equilibrium condition can be expressed in the (Y,i) space of IS-LM.
We still need to relate the exchange rate e to these variables
Reminder: the balance of payments is the sum of the current account and the capital account:
eiKAeYYCAeiYYBP ,,,,,, **
eYYCAeiKA ,,, *
From IS-LM to Mundell-Fleming
The capital account (KA) Is in surplus if the inflows of
capital are larger than the outflows.
Is in deficit in the other case. What determines these
capital flows ?
Intuitive answer: the earnings on savings If savings earn a higher return in Europe compared to
the USA, one would expect American capital to flow towards Europe.
From IS-LM to Mundell-Fleming
Investors choose between assets that pay different interest rates in different currencies.
What is the expected return for each of the possible investment? Their decision needs to account for the interest
rate differentials… …But also for the evolution of the exchange
rates between currencies.
This arbitrage mechanism produces what is called the uncovered interest rate parity (UIRP) This gives us a relation between interest rate
differentials and changes in the exchange rate
From IS-LM to Mundell-Fleming
You are a European investor with capital K (in €) looking for a 1-year investment.You can invest in €-denominated bonds,
and after a year you earn:
Or you can buy $-denominated US bonds: Step 1: you first convert your capital into dollars:
Step 2: after a year, you’ve earned (in dollars):
€1 iK
€/$eK
$€/$ 1 ieK
From IS-LM to Mundell-Fleming
But you need to bring you investment back home ! In other words you need to convert your
capital in $ back into €. In the mean time the $/€ exchange rate may
have changedStep 3: you convert your investment into €
You are indifferent if the 2 returns are equal
$/ € $
$/ €
1E
K e i
e
From IS-LM to Mundell-Fleming
You’re indifferent between $ and € assets if:
Rearranging gives:
If the exchange rate is not too volatile, this can be expressed as:
$/ € $€
$/ €
11
E
K e iK i
e
$/ €€ $
$/ €
1 1E
ei i
e $/ €€
$ $/ €
1
1 E
ei
i e
$/ € $/ €€ $
$/ €
Ee ei i
e
From IS-LM to Mundell-Fleming
Let’s summarise: Capital flows ensure an equalisation of interest rates expressed in the same currency
If the home interest rate is higher than world interest rate, zero net capital flows between countries requires investors to be expecting a depreciation of the home currency. If this is not the case, then capital will flow into the
home country, appreciating e until depreciation expectations occur
Only if the home rate equals the foreign rate will depreciation/appreciation expectations be zero (equilibrium)
Home interest rate
World interest rate
Expected exchange rate depreciation
$/ € $/ €€ $
$/ €
Ee ei i
e
From IS-LM to Mundell-Fleming
On BP the balance of payments is in equilibrium
BP
i
Y
BP is upward-sloping An increase in Y leads to
a BoP deficit (CA deficit) Returning to equilibrium
requires a KA surplus, and hence a higher i
The slope depends on the international mobility of capital The lower capital
mobility, the larger the slope of BP.
BoP surplusAppreciation of e
BoP deficitDepreciation of e
CA deficit
KA surplus
From IS-LM to Mundell-Fleming
The MF model was developed in the 60’s, when capital mobility was low (Bretton Woods)
i
Y
As a simplification, nowadays we assume perfect capital mobility
However, this remains a simplification! For certain cases (like
the case of trade with China), The concept of imperfect capital mobility remains relevant.
BPi*
Perfect capital mobility
i=i*
BoP DeficitDepreciation of e
BoP SurplusAppreciation of e
From IS-LM to Mundell-Fleming
BP
i
Y
i*
We now have 3 curves, IS-LM-BP :
IS
LM
The Mundell-Fleming model
From IS-LM to the Mundell-Fleming model
Effectiveness of policy
The effectiveness of policy
We now move to assessing the effectiveness of policy under the possible exchange rate settings:
Fixed exchange
rate
Flexible exchange
rate
Fiscal Policy ?? ??
Monetary Policy ?? ??
The effectiveness of policy
BP
i
Y
LM shifts to the right The increase in the money
supply lowers the rate of interest, leading to depreciation pressures on e
i*
Monetary policy with fixed exchange rate:
IS
LM
Such a policy cannot be carried out in practice
In order to guarantee the fixed exchange rate the CB must immediately increase i to i=i* by reducing money supply
The effectiveness of policy
BP
i
Y
IS shifts to the right: The crowding out effect
increases the rate of interest, creating appreciation pressures on e
i*
Fiscal policy with fixed exchange rate:
IS
LM
Policy is effective in increasing Y
In order to guarantee the fixed exchange rate the CB must immediately reduce i to i=i* by increasing money supply
The effectiveness of policy
BP
i
Y
LM shifts to the right The interest rate falls, which
leads to a depreciation of the exchange rate e
i*
Monetary policy with flexible exchange rate:
IS
LM
Policy is effective
The depreciation of the exchange rate stimulates exports and penalises imports As a resut IS shifts to the
right
The effectiveness of policy
BP
i
Y
IS shifts to the right The Central Bank doesn’t
have to react: The interest rate increases and the exchange rate appreciates
i*
Fiscal policy with flexible exchange rate:
IS
LM
Policy is ineffective
The appreciation of the exchange rate penalises exports and stimulates imports IS shifts left
The effectiveness of policy
Even with this simple example (assumption of perfect capital mobility), one can see that the effectiveness of policy depends on international conditions!
Fixed exchange
rate
Flexible exchange
rate
Fiscal Policy Effective Ineffective
Monetary Policy Impossible Effective
Summarising all this:
The effectiveness of policy
IncompatibilityTriangle
(Mundell)
FinancialAutarky
MonetaryUnion
FlexibleExchange rate
Autonomous monetary policy
Fixe
d ex
chan
ge rat
e Capital m
obility
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