Transcript Mankiw 5/e Chapter 11: Aggregate Demand II

Econ 101: Intermediate
Macroeconomic Theory
Larry Hu
Lecture 12: Application of IS-LM Model and
Great Depression
CHAPTER 11
Aggregate Demand II
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Equilibrium in the IS-LM Model
The IS curve represents
equilibrium in the goods
market.
Y  C (Y T )  I (r )  G
r
LM
The LM curve represents r1
money market equilibrium.
IS
M P  L(r ,Y )
Y1
The intersection determines
the unique combination of Y and r
that satisfies equilibrium in both markets.
CHAPTER 11
Aggregate Demand II
Y
slide 1
Interaction between
monetary & fiscal policy
 Model:
monetary & fiscal policy variables
(M, G and T ) are exogenous
 Real world:
Monetary policymakers may adjust M
in response to changes in fiscal policy,
or vice versa.
 Such interaction may alter the impact of
the original policy change.
CHAPTER 11
Aggregate Demand II
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The Fed’s response to G > 0
 Suppose Congress increases G.
 Possible Fed responses:
1. hold M constant
2. hold r constant
3. hold Y constant
 In each case, the effects of the G
are different:
CHAPTER 11
Aggregate Demand II
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Response 1: hold M constant
If Congress raises G,
the IS curve shifts
right
If Fed holds M
constant, then LM
curve doesn’t shift.
r
LM1
r2
r1
IS2
IS1
Results:
Y  Y2  Y1
Y1 Y2
Y
r  r2  r1
CHAPTER 11
Aggregate Demand II
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Response 2: hold r constant
If Congress raises G,
the IS curve shifts
right
r
To keep r constant,
Fed increases M to
shift LM curve right.
r2
r1
LM1
IS2
IS1
Results:
Y  Y3  Y1
LM2
Y1 Y2 Y3
Y
r  0
CHAPTER 11
Aggregate Demand II
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Response 3: hold Y constant
If Congress raises G,
the IS curve shifts
right
To keep Y constant,
Fed reduces M to
shift LM curve left.
LM2
LM1
r
r3
r2
r1
IS2
IS1
Results:
Y  0
Y1 Y2
Y
r  r3  r1
CHAPTER 11
Aggregate Demand II
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What is the Fed’s policy instrument?
Why does the Fed target interest rates
instead of the money supply?
1) They are easier to measure than the
money supply
2) The Fed might believe that LM shocks are
more prevalent than IS shocks. If so, then
targeting the interest rate stabilizes income
better than targeting the money supply.
(See Problem 7 on p.306)
CHAPTER 11
Aggregate Demand II
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CHAPTER 11
Aggregate Demand II
slide 8
CHAPTER 11
Aggregate Demand II
slide 9
CHAPTER 11
Aggregate Demand II
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IS-LM and Aggregate Demand
 So far, we’ve been using the IS-LM model
to analyze the short run, when the price
level is assumed fixed.
 However, a change in P would shift the LM
curve and therefore affect Y.
 The aggregate demand curve
(introduced in chap. 9 ) captures this
relationship between P and Y
CHAPTER 11
Aggregate Demand II
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Deriving the AD curve
Intuition for slope
of AD curve:
P  (M/P )
 LM shifts left
 r
 I
 Y
r
LM(P2)
LM(P1)
r2
r1
IS
P
Y2
Y
P2
P1
AD
Y2
CHAPTER 11
Y1
Aggregate Demand II
Y1
Y
slide 12
Monetary policy and the AD curve
The Fed can increase
aggregate demand:
M  LM shifts right
r
LM(M1/P1)
LM(M2/P1)
r1
r2
IS
 r
 I
P
 Y at each
value of P
P1
Y1
Y1
CHAPTER 11
Aggregate Demand II
Y2
Y2
Y
AD2
AD1
Y
slide 13
Fiscal policy and the AD curve
Expansionary fiscal policy
(G and/or T )
increases agg. demand:
r
LM
r2
r1
IS2
T  C
IS1
 IS shifts right
P
Y1
Y2
Y
 Y at each
value
P1
of P
Y1
CHAPTER 11
Aggregate Demand II
Y2
AD2
AD1
Y
slide 14
IS-LM and AD-AS
in the short run & long run
Recall from Chapter 9:
The force that moves
the economy from the short run to the long run
is the gradual adjustment of prices.
In the short-run
equilibrium, if
then over time,
the price level will
Y Y
Y Y
rise
Y Y
remain constant
CHAPTER 11
fall
Aggregate Demand II
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The SR and LR effects of an IS shock
r
A negative IS shock
shifts IS and AD left,
causing Y to fall.
LRAS LM(P )
1
IS2
Y
P
SRAS1
Y
Aggregate Demand II
Y
LRAS
P1
CHAPTER 11
IS1
AD1
AD2
Y
slide 16
The SR and LR effects of an IS shock
r
LRAS LM(P )
1
In the new short-run
equilibrium, Y  Y
IS2
Y
P
SRAS1
Y
Aggregate Demand II
Y
LRAS
P1
CHAPTER 11
IS1
AD1
AD2
Y
slide 17
The SR and LR effects of an IS shock
r
LRAS LM(P )
1
In the new short-run
equilibrium, Y  Y
IS2
Over time,
P gradually falls,
which causes
• SRAS to move down
• M/P to increase,
which causes LM
to move down
CHAPTER 11
Y
P
Y
LRAS
P1
Aggregate Demand II
IS1
SRAS1
Y
AD1
AD2
Y
slide 18
The SR and LR effects of an IS shock
r
LRAS LM(P )
1
LM(P2)
IS2
Over time,
P gradually falls,
which causes
• SRAS to move down
• M/P to increase,
which causes LM
to move down
CHAPTER 11
Y
P
IS1
Y
LRAS
P1
SRAS1
P2
SRAS2
Aggregate Demand II
Y
AD1
AD2
Y
slide 19
The SR and LR effects of an IS shock
r
LRAS LM(P )
1
LM(P2)
This process continues
until economy reaches
a long-run equilibrium
with
Y Y
IS2
Y
P
Y
LRAS
P1
SRAS1
P2
SRAS2
Y
CHAPTER 11
IS1
Aggregate Demand II
AD1
AD2
Y
slide 20
The Great Depression
220
billions of 1958 dollars
30
Unemployment
(right scale)
25
200
20
180
15
160
10
Real GNP
(left scale)
140
120
1929
percent of labor force
240
5
0
1931
CHAPTER 11
1933
1935
Aggregate Demand II
1937
1939
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The Spending Hypothesis:
Shocks to the IS Curve
 asserts that the Depression was largely due
to an exogenous fall in the demand for
goods & services -- a leftward shift of the IS
curve
 evidence:
output and interest rates both fell, which is
what a leftward IS shift would cause
CHAPTER 11
Aggregate Demand II
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The Spending Hypothesis:
Reasons for the IS shift
1. Stock market crash  exogenous C
 Oct-Dec 1929: S&P 500 fell 17%
 Oct 1929-Dec 1933: S&P 500 fell 71%
2. Drop in investment
 “correction” after overbuilding in the 1920s
 widespread bank failures made it harder to
obtain financing for investment
3. Contractionary fiscal policy
 in the face of falling tax revenues and
increasing deficits, politicians raised tax rates
and cut spending
CHAPTER 11
Aggregate Demand II
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The Money Hypothesis:
A Shock to the LM Curve
 asserts that the Depression was
largely due to huge fall in the money
supply
 evidence:
M1 fell 25% during 1929-33.
CHAPTER 11
Aggregate Demand II
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The Money Hypothesis Again:
The Effects of Falling Prices
 asserts that the severity of the Depression
was due to a huge deflation:
P fell 25% during 1929-33.
 This deflation was probably caused by
the fall in M, so perhaps money played
an important role after all.
 In what ways does a deflation affect the
economy?
CHAPTER 11
Aggregate Demand II
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The Money Hypothesis Again:
The Effects of Falling Prices
The stabilizing effects of deflation:
 P  (M/P )  LM shifts right  Y
 Pigou effect:
P  (M/P )
 consumers’ wealth 
 C
 IS shifts right
 Y
CHAPTER 11
Aggregate Demand II
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The Money Hypothesis Again:
The Effects of Falling Prices
The destabilizing effects of unexpected deflation:
debt-deflation theory
P (if unexpected)
 transfers purchasing power from borrowers
to lenders
 borrowers spend less,
lenders spend more
 if borrowers’ propensity to spend is larger
than lenders, then aggregate spending falls,
the IS curve shifts left, and Y falls
CHAPTER 11
Aggregate Demand II
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The Money Hypothesis Again:
The Effects of Falling Prices
The destabilizing effects of expected deflation:
e




r  for each value of i
I  because I = I (r )
planned expenditure & agg. demand 
income & output 
CHAPTER 11
Aggregate Demand II
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Liquidity Trap
IS-LM: monetary policy
increase investment by
reducing interest rate
r
When interest rate is low, it
may not work, just like
today
IS
LM
Y
CHAPTER 11
Aggregate Demand II
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Liquidity Trap
IS
The policy maker can
create inflation
expectationi = r + 
r
Nominal interest rate
never below zero
If inflation is zero, real
interest rate never falls
below zero
LM1
IS
LM2
Y
If inflation if 3%, real
interest rate can be 3%
CHAPTER 11
Aggregate Demand II
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