Lecture 9
21.4.2015
Aggregate Demand
and Aggregate
Supply
Copyright © 2004 South-Western
Previous lecture
• Construct Macroeconomic model of an Open
Economy
• Model of the market for loanable funds
• Model of the foreign-currency exchange market
• EQUILIBRIUM in an Open Economy
• Policies and events that effect the Equilibrium
• Government budget deficits
• Trade policies
• Political and economic instability
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Short-Run Economic Fluctuations
• Economic activity fluctuates from year to year.
• In most years production of goods and services
rises.
• On average over the past 50 years, production in the
U.S. economy has grown by about 3 percent per
year.
• In some years normal growth does not occur,
causing a recession.
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Short-Run Economic Fluctuations
• A recession is a period of declining real
incomes, and rising unemployment.
• A depression is a severe recession.
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Outline
• Economic activity in the short-run
• Economic Fluctuations or the Business Cycles
• What causes short-run fluctuations?
• What can be done to prevent periods of falling
incomes and rising unemployment?
• How can policymakers reduce the length and
severity of recessions?
• GDP, unemployment, real interest rate…
• Short-run fluctuations from long-run trends
• The model of aggregate demand and supply
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THREE KEY FACTS ABOUT
ECONOMIC FLUCTUATIONS
• Economic fluctuations are irregular and
unpredictable.
• Fluctuations in the economy are often called the
business cycle.
Figure 1 A Look At Short-Run Economic
Fluctuations
Billions of
1996 Dollars
Real GDP
(a) Real GDP
$10,000
9,000
8,000
7,000
6,000
5,000
4,000
3,000
2,000
1965 1970 1975 1980 1985 1990 1995 2000
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Copyright © 2004 South-Western
THREE KEY FACTS ABOUT
ECONOMIC FLUCTUATIONS
• Most macroeconomic variables fluctuate
together.
• Most macroeconomic variables that measure some
type of income or production fluctuate closely
together.
• Although many macroeconomic variables fluctuate
together, they fluctuate by different amounts.
Figure 1 A Look At Short-Run Economic
Fluctuations
Billions of
1996 Dollars
(b) Investment Spending
$1,800
1,600
1,400
1,200
1,000
800
600
400
200
1965 1970 1975 1980 1985 1990 1995 2000
Investment spending
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Copyright © 2004 South-Western
THREE KEY FACTS ABOUT
ECONOMIC FLUCTUATIONS
• As output falls, unemployment rises.
• Changes in real GDP are inversely related to
changes in the unemployment rate.
• During times of recession, unemployment rises
substantially.
Figure 1 A Look At Short-Run Economic
Fluctuations
Percent of
Labor Force
(c) Unemployment Rate
0
2
4
6
8
10
12
1965 1970 1975 1980 1985 1990 1995 2000
Unemployment rate
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Copyright © 2004 South-Western
EXPLAINING SHORT-RUN
ECONOMIC FLUCTUATIONS
• How the Short Run Differs from the Long Run
• Most economists believe that classical theory
describes the world in the long run but not in the
short run.
• Changes in the money supply affect nominal variables
but not real variables in the long run.
• The assumption of monetary neutrality is not appropriate
when studying year-to-year changes in the economy.
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The Basic Model of Economic Fluctuations
• Two variables are used to develop a model to
analyze the short-run fluctuations.
• The economy’s output of goods and services
measured by real GDP.
• The overall price level measured by the CPI or the
GDP deflator.
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The Basic Model of Economic Fluctuations
• The Basic Model of Aggregate Demand and
Aggregate Supply
• Economist use the model of aggregate demand and
aggregate supply to explain short-run fluctuations
in economic activity around its long-run trend.
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The Basic Model of Economic Fluctuations
• The Basic Model of Aggregate Demand and
Aggregate Supply
• The aggregate-demand curve shows the quantity of
goods and services that households, firms, and the
government want to buy at each price level.
• The aggregate-supply curve shows the quantity of
goods and services that firms choose to produce and
sell at each price level.
Figure 2 Aggregate Demand and Aggregate
Supply...
Quantity of
Output
Price
Level
0
Aggregate
supply
Aggregate
demand
Equilibrium
output
Equilibrium
price level
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Figure 3 The Aggregate-Demand Curve...
Quantity of
Output
Price
Level
0
Aggregate
demand
P
Y Y2
P2
1. A decrease
in the price
level . . .
2. . . . increases the quantity of
goods and services demanded.
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Copyright © 2004 South-Western
THE AGGREGATE-DEMAND
CURVE
• The four components of GDP (Y) contribute to
the aggregate demand for goods and services.
Y = C + I + G + NX
• How the price level effects the quantity of
goods and services demanded for consumption,
investment, and net exports (G is fixed)
• 3 effects
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Why the Aggregate-Demand Curve Is
Downward Sloping
• The Price Level and Consumption: The Wealth
Effect
• The Price Level and Investment: The Interest
Rate Effect
• The Price Level and Net Exports: The
Exchange-Rate Effect
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Why the Aggregate-Demand Curve Is
Downward Sloping
• The Price Level and Consumption: The Wealth
Effect
• A decrease in the price level makes consumers feel
more wealthy, which in turn encourages them to
spend more.
• This increase in consumer spending means larger
quantities of goods and services demanded.
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Why the Aggregate-Demand Curve Is
Downward Sloping
• The Price Level and Investment: The Interest
Rate Effect
• A lower price level reduces the interest rate, which
encourages greater spending on investment goods.
• This increase in investment spending means a larger
quantity of goods and services demanded.
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Why the Aggregate-Demand Curve Is
Downward Sloping
• The Price Level and Net Exports: The
Exchange-Rate Effect
• When a fall in the U.S. price level causes U.S.
interest rates to fall, the real exchange rate
depreciates, which stimulates U.S. net exports.
• The increase in net export spending means a larger
quantity of goods and services demanded.
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Why the Aggregate-Demand Curve Might
Shift
• The downward slope of the aggregate demand
curve shows that a fall in the price level raises
the overall quantity of goods and services
demanded.
• Consumers are wealthier – stimulates the demand
for consumption goods
• Interest rate falls – stimulates the demand for
investment goods
• The currency depreciates – stimulates the demand
for net exports
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Why the Aggregate-Demand Curve Might
Shift
• Shifts arising from
• Consumption
• Investment
• Government Purchases
• Net Exports
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Shifts in the Aggregate Demand
Curve
Quantity of
Output
Price
Level
0
Aggregate
demand, D1
P1
Y1
D2
Y2
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THE AGGREGATE-SUPPLY
CURVE
• In the long run, the aggregate-supply curve is
vertical.
• In the short run, the aggregate-supply curve is
upward sloping.
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THE AGGREGATE-SUPPLY
CURVE
• The Long-Run Aggregate-Supply Curve
• In the long run, an economy’s production of goods
and services depends on its supplies of labor,
capital, and natural resources and on the available
technology used to turn these factors of production
into goods and services.
• The price level does not affect these variables in the
long run.
Figure 4 The Long-Run Aggregate-Supply Curve
Quantity of
Output
Natural rate
of output
Price
Level
0
Long-run
aggregate
supply
P2
1. A change
in the price
level . . .
2. . . . does not affect
the quantity of goods
and services supplied
in the long run.
P
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Copyright © 2004 South-Western
THE AGGREGATE-SUPPLY
CURVE
• The Long-Run Aggregate-Supply Curve
• The long-run aggregate-supply curve is vertical at
the natural rate of output.
• This level of production is also referred to as
potential output or full-employment output.
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Why the Long-Run Aggregate-Supply Curve
Might Shift
• Any change in the economy that alters the
natural rate of output shifts the long-run
aggregate-supply curve.
• The shifts may be categorized according to the
various factors in the classical model that affect
output.
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Why the Long-Run Aggregate-Supply Curve
Might Shift
• Shifts arising
• Labor
• Capital
• Natural Resources
• Technological Knowledge
Figure 5 Long-Run Growth and Inflation
Quantity of
Output
Y1980
AD1980
AD1990
Aggregate
Demand, AD2000
Price
Level
0
Long-run
aggregate
supply,
LRAS1980
Y1990
LRAS1990
Y2000
LRAS2000
P1980
1. In the long run,
technological
progress shifts
long-run aggregate
supply . . .
4. . . . and
ongoing inflation.
3. . . . leading to growth
in output . . .
P1990
P2000
2. . . . and growth in the
money supply shifts
aggregate demand . . .
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Copyright © 2004 South-Western
A New Way to Depict Long-Run Growth and
Inflation
• Short-run fluctuations in output and price level
should be viewed as deviations from the
continuing long-run trends.
• In the short run, an increase in the overall level
of prices in the economy tends to raise the
quantity of goods and services supplied.
• A decrease in the level of prices tends to reduce
the quantity of goods and services supplied.
Figure 6 The Short-Run Aggregate-Supply Curve
Quantity of
Output
Price
Level
0
Short-run
aggregate
supply
1. A decrease
in the price
level . . .
2. . . . reduces the quantity
of goods and services
supplied in the short run.
Y
P
Y2
P2
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Copyright © 2004 South-Western
Why the Aggregate-Supply Curve Slopes
Upward in the Short Run
• The Sticky-Wage Theory
• The Sticky-Price Theory
• The Misperceptions Theory
• Common feature
The quantity of output supplied deviates from its longrun
level when the actual price level in the economy
deviates from the price level that people expected to
prevail.
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Why the Aggregate-Supply Curve Slopes
Upward in the Short Run
• The Sticky-Wage Theory
• Nominal wages are slow to adjust, or are “sticky” in
the short run:
• Wages do not adjust immediately to a fall in the price
level.
• A lower price level makes employment and production
less profitable.
• This induces firms to reduce the quantity of goods and
services supplied.
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• The Sticky-Price Theory
• Prices of some goods and services adjust sluggishly
in response to changing economic conditions:
• An unexpected fall in the price level leaves some firms
with higher-than-desired prices.
• This depresses sales, which induces firms to reduce the
quantity of goods and services they produce.
Why the Aggregate-Supply Curve Slopes
Upward in the Short Run
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Why the Aggregate-Supply Curve Slopes
Upward in the Short Run
• The Misperceptions Theory
• Changes in the overall price level temporarily
mislead suppliers about what is happening in the
markets in which they sell their output:
• A lower price level causes misperceptions about
relative prices.
• These misperceptions induce suppliers to decrease the
quantity of goods and services supplied.
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Why the Short-Run Aggregate-Supply Curve
Might Shift
• Shifts arising
• Labor
• Capital
• Natural Resources.
• Technology.
• Expected Price Level.
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Why the Aggregate Supply Curve Might Shift
• An increase in the expected price level reduces
the quantity of goods and services supplied and
shifts the short-run aggregate supply curve to
the left.
• A decrease in the expected price level raises the
quantity of goods and services supplied and
shifts the short-run aggregate supply curve to
the right.
Figure 7 The Long-Run Equilibrium
Natural rate
of output
Quantity of
Output
Price
Level
0
Short-run
aggregate
supply
Long-run
aggregate
supply
Aggregate
demand
AEquilibrium
price
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Figure 8 A Contraction in Aggregate Demand
Quantity of
Output
Price
Level
0
Short-run aggregate
supply, AS
Long-run
aggregate
supply
Aggregate
demand, AD
AP
Y
AD2
AS2
1. A decrease in
aggregate demand . . .
2. . . . causes output to fall in the short run . . .
3. . . . but over
time, the short-run
aggregate-supply
curve shifts . . .
4. . . . and output returns
to its natural rate.
CP3
BP2
Y2
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Copyright © 2004 South-Western
TWO CAUSES OF ECONOMIC
FLUCTUATIONS
• Shifts in Aggregate Demand
• In the short run, shifts in aggregate demand cause
fluctuations in the economy’s output of goods and
services.
• In the long run, shifts in aggregate demand affect
the overall price level but do not affect output.
Figure 10 An Adverse Shift in Aggregate Supply
Quantity of
Output
Price
Level
0
Aggregate demand
3. . . . and
the price
level to rise.
2. . . . causes output to fall . . .
1. An adverse shift in the shortrun
aggregate-supply curve . . .
Short-run
aggregate
supply, AS
Long-run
aggregate
supply
Y
A
P
AS2
B
Y2
P2
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Copyright © 2004 South-Western
TWO CAUSES OF ECONOMIC
FLUCTUATIONS
• An Adverse Shift in Aggregate Supply
• A decrease in one of the determinants of aggregate
supply shifts the curve to the left:
• Output falls below the natural rate of employment.
• Unemployment rises.
• The price level rises.
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The Effects of a Shift in Aggregate Supply
• Stagflation
• Adverse shifts in aggregate supply cause
stagflation—a period of recession and inflation.
• Output falls and prices rise.
• Policymakers who can influence aggregate demand
cannot offset both of these adverse effects
simultaneously.
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The Effects of a Shift in Aggregate Supply
• Policy Responses to Recession
• Policymakers may respond to a recession in one of
the following ways:
• Do nothing and wait for prices and wages to adjust.
• Take action to increase aggregate demand by using
monetary and fiscal policy.
Figure 11 Accommodating an Adverse Shift in
Aggregate Supply
Quantity of
Output
Natural rate
of output
Price
Level
0
Short-run
aggregate
supply, AS
Long-run
aggregate
supply
Aggregate demand, AD
P2
A
P
AS2
3. . . . which
causes the
price level
to rise
further . . .
4. . . . but keeps output
at its natural rate.
2. . . . policymakers can
accommodate the shift
by expanding aggregate
demand . . .
1. When short-run aggregate
supply falls . . .
AD2
CP3
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Copyright © 2004 South-Western
Summary
• All societies experience short-run economic
fluctuations around long-run trends.
• These fluctuations are irregular and largely
unpredictable.
• When recessions occur, real GDP and other
measures of income, spending, and production
fall, and unemployment rises.
Copyright © 2004 South-Western
Summary
• Economists analyze short-run economic
fluctuations using the aggregate demand and
aggregate supply model.
• According to the model of aggregate demand
and aggregate supply, the output of goods and
services and the overall level of prices adjust to
balance aggregate demand and aggregate
supply.
Copyright © 2004 South-Western
Summary
• The aggregate-demand curve slopes downward
for three reasons: a wealth effect, an interest
rate effect, and an exchange rate effect.
• Any event or policy that changes consumption,
investment, government purchases, or net
exports at a given price level will shift the
aggregate-demand curve.
Copyright © 2004 South-Western
Summary
• In the long run, the aggregate supply curve is
vertical.
• The short-run, the aggregate supply curve is
upward sloping.
• The are three theories explaining the upward
slope of short-run aggregate supply: the
misperceptions theory, the sticky-wage theory,
and the sticky-price theory.
Copyright © 2004 South-Western
Summary
• Events that alter the economy’s ability to
produce output will shift the short-run
aggregate-supply curve.
• Also, the position of the short-run aggregatesupply
curve depends on the expected price
level.
• One possible cause of economic fluctuations is
a shift in aggregate demand.
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Summary
• A second possible cause of economic
fluctuations is a shift in aggregate supply.
• Stagflation is a period of falling output and
rising prices.