• What the components of aggregate demand (AD) are and why the AD curve slopes downward.
• What the components of aggregate supply (AS) are and why the AS curve slopes upward.
• What factors shift AD and AS.
• What differences exist between the short and long run.
• What the short‐ and long‐run effects of shifts in AD and AS are.
• What policy options are available to counteract shocks.
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11© 2014 by McGraw‐Hill Education
Chapter 28
Aggregate Demand and Aggregate Supply
2© 2014 by McGraw‐Hill Education
• What the components of aggregate demand (AD)
are and why the AD curve slopes downward.
• What the components of aggregate supply (AS)
are and why the AS curve slopes upward.
• What factors shift AD and AS.
• What differences exist between the short and
long run.
• What the short‐ and long‐run effects of shifts in
AD and AS are.
• What policy options are available to counteract
shocks.
What will you learn in this chapter?
3© 2014 by McGraw‐Hill Education
• The last three chapters have focused separately
on three features of the economy:
1. Output (GDP).
2. Prices.
3. Unemployment.
• These factors do not fluctuate independently.
• A demand and supply model for the
macroeconomy would be useful.
• The model of aggregate demand and aggregate
supply shows how output, prices, and
employment are all tied together as part of a
single economic equilibrium.
Tying it all together
24© 2014 by McGraw‐Hill Education
Aggregate demand
• Aggregate demand is equal to GDP, or AD = GDP = C + I + G + NX.
• The aggregate demand curve shows the relationship between the
overall price level in the economy and output.
Aggregate demand
Price level
Output
1P
Y1
1. A decrease
in the price
level
P2
Y2
2. increases the amount of
goods and services
demanded.
• We are interested in what
happens when the prices
of all goods go up or
down.
• Price changes are
measured by the price
index or inflation.
5© 2014 by McGraw‐Hill Education
• Why the AD curve slopes downward is due to
each component of AD.
1. Consumption (C):
• As prices rise, people reduce consumption
because their real wealth decreases.
– This is called the wealth effect.
2. Investment (I):
• As prices rise, interest rates rise.
• This causes borrowing to decrease and results
in a decrease in investment spending.
Why does the AD curve slope downward?
6© 2014 by McGraw‐Hill Education
3. Government spending (G):
• Most government spending is independent of
the price level.
• Government spending does not contribute to a
downward sloping AD.
4. Net exports (NX):
• When U.S. prices increase, U.S. goods become
relatively more expensive compared to other
countries’ goods.
• Imports increase and exports decrease.
• As price levels increase, net exports decrease.
Why does the AD curve slope downward?
37© 2014 by McGraw‐Hill Education
• There is a negative relationship between the price
level and three of the national expenditure
components:
1. Consumption – negative relationship.
2. Investment – negative relationship.
3. Government spending – no relationship.
4. Net exports – negative relationship.
• This causes a negative relationship between the
price level and aggregate expenditures.
Why does the AD curve slope downward?
8© 2014 by McGraw‐Hill Education
The entire aggregate demand curve can also shift in response to non‐
price changes in any of the four components of aggregate demand.
Shifting the aggregate demand curve
1
Price level
Output
AD
A rightward shift of aggregate demand
Price level
A leftward shift of aggregate demand
AD1
Output
AD2
AD2
• When a non‐price factor increases a
component of AD, the entire AD curve
shifts to the right.
• GDP is higher at every price level.
• When a non‐price factor decreases a
component of AD, the entire AD
curve shifts to the left.
• GDP is lower at every price level.
9© 2014 by McGraw‐Hill Education
Category Increase (shift right) Decrease (shift left)
Consumption
• High expectations about future income
increase consumer spending.
• Tax cuts increase consumer spending.
• Low expectations about future income
lead to greater saving and less spending.
• Higher interest rates discourage
borrowing.
Investment
• Confidence in the future of the economy
leads firms to expand their businesses.
• A tax credit for small businesses inspires
firms to buy new company cars.
• Firms cut back on spending in order to
weather a recession.
• Taxes on capital increase, leaving less
money for investment.
Government spending
• Increase in government spending spurs
spending after a recession.
• Decrease in government spending in
response to concerns about increasing
debt leads to less spending.
Net exports
• A new free trade agreement with Europe
reduces most tariffs and other restrictions
on U.S. goods.
• Economic growth abroad in China
increases demand for U.S. goods and
services.
• Other countries increase their tariffs on
U.S. goods, making the goods more
expensive.
• The dollar strengthens, making U.S. goods
and services more expensive for
international consumers, decreasing
demand.
The main non‐price factors are as follows:
Shifting the aggregate demand curve
410© 2014 by McGraw‐Hill Education
Indicate whether each of the following situations results in
an increase or decrease in aggregate demand.
Active Learning: AD shifts
1. Consumers feel confident that incomes will
increase significantly in the next year.
2. The government is concerned about
increasing its debt and thus reduces
government spending.
3. China increases the tariffs on U.S. goods.
4. The government awards small factories a
tax credit, which many use to build new
manufacturing plants.
11© 2014 by McGraw‐Hill Education
• Aggregate supply is the sum total of the production of all
the firms in the economy
• The aggregate supply curve shows the relationship
between the overall price level in the economy and total
production by firms.
• The AS curve represents production in the economy as a
whole, not just of one good or service. It describes how
much firms decide to produce.
• The economy operates differently in the short run and
long run, so there are two different AS curves.
• The long‐run aggregate supply curve (LRAS).
• The short‐run aggregate supply curve (SRAS).
Aggregate supply
12© 2014 by McGraw‐Hill Education
In the short run, the AS curve slopes upward.
Short‐run aggregate supply (SRAS)
P1
Y1 Y2
P2
Price level
Output
Short-run aggregate
supply (SRAS)
• Prices of final goods
increase more quickly
than input prices.
• An increase in the final
goods’ price level
increases firms’ profits.
• Firms respond by
increasing production.
513© 2014 by McGraw‐Hill Education
• The long run is not a set amount of time.
– It is the time required for input prices to fully adjust to economic
conditions.
• When input costs adjust, firms no longer earn positive economic
profits.
• The economy returns to where it started.
• Changes in the price‐level do not affect aggregate supply in the long
run.
Long‐run aggregate supply (LRAS)
Price level
Output
Long-run aggregate
supply (LRAS)
Yp
P1
P2
• In the long run, the aggregate
supply curve is fixed.
• The long‐run aggregate supply
curve is not affected by the
price level, causing it to be
vertical.
• The LRAS curve represents
potential output in the
economy.
14© 2014 by McGraw‐Hill Education
• Economies do not always produce to their potential output.
• Business cycles are fluctuations of output around the level of potential
output.
– When output is higher than potential output, the economy is in a boom.
– When output is below potential output, the economy is in a recession.
• The U.S. business cycle has occurred frequently over the last 50 years.
The business cycle
Long-run
average
growth
-4
-2
0
2
4
6
8
1960 1970 1980 1990 2000 2010
Year
Percent Annual growth rate of
real per capita GDP
The average real GDP per
capita growth rate was
around 3% between 1960
and 2010.
But notice that the yearly
average fluctuated quite a bit.
15© 2014 by McGraw‐Hill Education
If inputs become more expensive, firms will want to
supply fewer goods at any price level in the short‐run.
Shifts in the SRAS curve
SRAS1
SRAS2
Price level
LRAS
Output
• The SRAS curve
shifts to the left.
• Supply shocks are
significant events
that directly affect
production and the
AS curve in the
short run.
616© 2014 by McGraw‐Hill Education
In the long run, production decisions are influenced
by inputs, regardless of the overall price level.
Shifts in the LRAS curve
LRAS2020
(2010)
Y
(2020)
LRAS
2010
Price level
OutputYp p
• The LRAS curve shifts
outward if there is an
increase in available
inputs.
• Everything that shifts
the LRAS also shifts the
SRAS.
17© 2014 by McGraw‐Hill Education
Shifts in the LRAS curve
Factor Increases LRAS Decreases LRAS
Technology
Technological innovation allows
for greater production using the
same amount of inputs.
A new law stripping away
intellectual property rights
reduces the incentive to
innovate.
Capital
Foreign investment in factories
and machines increases available
capital.
Depreciation and wear
breaks down capital.
Labor Immigration increases the availablesupply of labor.
Aging population takes
workers out of the labor force.
Education Universal primary education giveseveryone a chance to go to school.
Reduction of federal college
grants.
Natural resources
New energy sources allow factories
to produce more with the same
inputs.
Climate change permanently
reduces the amount of land
that can be farmed.
The main factors that shift LRAS are as follows.
18© 2014 by McGraw‐Hill Education
Equilibrium in the national economy is at the point
where AD = AS.
Economic fluctuations
SRAS
AD
LRAS
Y*
P*
Price level
Output
• Short‐run equilibrium occurs
at the intersection of the AD
and SRAS
• The long‐run equilibrium
occurs where the AD curve
crosses both the LRAS and
SRAS.
– Prices are at expected levels.
– The short run level of output
is the same as the long run
level of potential output.
719© 2014 by McGraw‐Hill Education
Using the AD‐AS model, the short‐ and long‐run effects of a
rightward shift in AD can be predicted.
Effects of a shift in aggregate demand
Short run
Price level
Output
LRAS
AD1
SRAS
Y1
E1P1
P2
AD2
Y2
Long run
Price level
Output
LRAS
2
E
E3
SRAS2
AD2
AD1
SRAS1
P1
P2
Y
1
E2
P3
Y3
• The increase in AD causes wages and
input prices to rise.
• SRAS decreases.
• Output returns to original level.
• Prices increase again.
E2
• Increase in consumer confidence
causes AD to increase.
• Output is above long‐run
potential.
• Prices increase.
20© 2014 by McGraw‐Hill Education
• Decrease in consumer confidence
causes AD to decrease..
• Output is below long run potential.
• Prices decrease.
Effects of a shift in aggregate demand
SRAS
AD1
LRAS
Short runPrice level
Output
2
AD2
P
Long runPrice level
Output
AD1
AD2
LRAS
SRAS1
E1P1
P2
• The decrease in AD causes wages and
input prices to fall.
• SRAS increases.
• Output returns to original level.
• Prices decrease again.
E1
Y1
P1
Y2
2E
Y2
2E
Y3
SRAS2
P3
E3
Using the AD‐AS model, the short‐ and long‐run effects of a
leftward shift in AD can be predicted.
21© 2014 by McGraw‐Hill Education
Changes in AD in the short and long run are
summarized as follows.
Effects of a shift in aggregate demand
Increase in AD
Increase in government
spending: increases G
Output increases.
Price increases.
Decrease in AD
Reduction in consumer
confidence: reduces C
Output decreases.
Price decreases.
Shift Example Short run Long run
Output unchanged.
Price increases.
Output unchanged.
Price decreases.
822© 2014 by McGraw‐Hill Education
• Temporary supply side shock causes
the SRAS to decrease.
• Output falls below long run potential.
• Prices increase.
Effects of a shift in aggregate supply
Short run
Output
SRAS2
2Y
P2
Output
Long run
Price level
LRAS
SRAS1
AD
Y2
P2
SRAS2
Y1
P1 E1
E2
• The decrease in SRAS causes wages to
fall (price of labor decreases).
• SRAS increases.
• Output increases to original level.
• Prices decrease to original level.
Price level
LRAS
SRAS1
AD
Y1
P1 E1
E2
Supply‐side shocks can also be analyzed. Suppose a temporary
supply‐side shock hits the economy.
23© 2014 by McGraw‐Hill Education
• Permanent supply side shock causes
the LRAS to decrease.
• Input prices rise causing the SRAS to
decrease.
• Prices increase and output decreases.
Effects of a shift in aggregate supply
• As prices continue to rise, the SRAS
decreases until it reaches the long run
equilibrium.
• Prices increase again.
• Output decreases to long‐run
equilibrium.
P1
Y1
P2
LRAS2
SRAS2
Y2 Output
P3
P1
Y1Y3
LRAS1LRAS2
SRAS1
Price level
AD
Long run
E1
SRAS3LRAS1
SRAS1
Price level
Output
AD
Short run
E1
E3
E2
Suppose a permanent supply‐side shock hits the economy.
24© 2014 by McGraw‐Hill Education
• The AD/AS model is a powerful tool for:
– Understanding overall economic conditions.
– Formulating policy responses to shocks.
• It is important to distinguish between supply
and demand shocks.
Comparing demand and supply shocks
Event What kind of shock?
Temporary increase in the price of oil Short-run supply shock
Technological innovation Long-run supply shock
Drop in consumer confidence Demand shock
Sudden increase in immigration Long-run supply shock
925© 2014 by McGraw‐Hill Education
Indicate what type of shock is caused by each of
the following situations.
Active Learning: Demand and supply shocks
Situation Type of Shock
Consumer confidence increases
A hurricane destroys many
factories on the east coast
There is a large surge in the
number of immigrants into the U.S.
The discovery of new oil reserves
causes a temporary decrease in
the price of oil
26© 2014 by McGraw‐Hill Education
• There are clear predictions about how different types of
shocks will affect prices and output.
• These predictions give clues to what type of shock
occurred.
Comparing demand and supply shocks
Supply or demand? Positive shock Negative shock
Demand side
Short-run:
Output increases
Price increases
Demand side
Long-run:
No change in output
Price increases
Temporary shock:
Supply side
Short-run:
Output increases
Price decreases
Temporary shock:
Supply side
Long-run:
No change in output
No change in price
Permanent shock:
Supply side
Long-run:
Output increases
Price decreases
Short-run:
Output decreases
Price decreases
Long-run:
No change in output
Price decreases
Short-run:
Output decreases
Price increases
Long-run:
No change in output
No change in price
Long-run:
Output decreases
Price increases
27© 2014 by McGraw‐Hill Education
For each of the following situations, indicate how the
AD/AS model predicts prices and output will change.
Active Learning: Short‐ and long‐run predictions
Situation Short run Long run
An increase in consumption
positive AD shock.
Unusually high rainfall increases
current year wheat crop yields
negative SRAS shock.
The FED increases interest rates
which discourages borrowing
negative AD shock.
10
28© 2014 by McGraw‐Hill Education
• It can take a long time for the economy to fully
adjust to demand and supply shocks.
• Waiting for adjustments is often difficult on
producers and consumers.
• Voters often call upon politicians to respond
during a recession.
• The government can try to boost the economy
out of a recession through government
spending.
The role of public policy
29© 2014 by McGraw‐Hill Education
• The government can try to counter this
negative demand shock by spending more to
cause aggregate demand to increase.
• Such policies are challenging to implement.
– It is difficult to gauge the overall effect of
government spending on AD.
– It is rare to perfectly design policy to restore AD to
its original level.
– Government intervention impacts the long‐run
outcomes.
The role of public policy
30© 2014 by McGraw‐Hill Education
The government may respond to a housing crisis as shown below.
Government spending to counter negative
demand shocks
AD2
1
AD2
AD1
Price level
Output
LRAS
SRAS
Government stimulus
Y3
P2
Y2
P2
AD3
P3
Y2
Price level
Output
LRAS
AD1
P
SRAS
Housing-market crash
Y1
E1
E2
E3
E2
• Government spending increases AD.
• Equilibrium price level increases.
• Output increases, but is still lower
than the original level.
• The crash of the housing market
causes AD to decrease.
• Short term price level falls.
• Short term output falls.
11
31© 2014 by McGraw‐Hill Education
• The drought causes SRAS to
decrease.
• Short term prices rise.
• Short term output falls.
Government spending to counter negative
supply shocks
• Government spending increases AD.
• New equilibrium prices are higher.
• Output increases to the original
level.
P1
Y1
SRAS1
AD
LRAS
Price level
Output
Drought shifts aggregate supply
P2
Y2
SRAS2
1
Price level
Output
Government response
AD2
SRAS1
SRAS2
AD1
LRAS
P3
Y1
E2
E1 E1
E3
P
P2
Y2
E2
The government may respond to Midwestern drought as shown below.
32© 2014 by McGraw‐Hill Education
• The long‐run result of government
intervention is higher prices, but output may
more quickly return to long‐run levels.
• Why would the government ever choose to
intervene?
– The speed of recovery could be slow otherwise.
– Lower prices are not always good for certain goods
and services.
• Government spending is a short‐term policy
action used to address short‐term shocks.
Government spending summarized
33© 2014 by McGraw‐Hill Education
• The AD/AS model helps to understand what
drives prices, unemployment, and GDP in
context of the economy.
• AD shows the relationship between overall
prices and total demand in the economy.
• AD is downward‐sloping because consumption,
investment, and net exports all decrease when
prices rise.
Summary
12
34© 2014 by McGraw‐Hill Education
• AS shows the relationship between overall
prices and total production.
• There are two supply curve: one for the short
run and one for the long run.
– The SRAS is upward‐sloping because it takes time
for prices and/or wages to adjust.
– The LRAS curve is vertical because supply doesn’t
depend on prices in the long run.
Summary
35© 2014 by McGraw‐Hill Education
• Positive AD shocks result in increased prices
and output in the short run.
– In the long run, output returns to its original level
and prices rise higher.
• Negative AD shocks result in lower prices and
output in the short run.
– In the long run, output returns to its original level
and prices fall further.
Summary
36© 2014 by McGraw‐Hill Education
• Prices and output only change in the long run
when there are permanent AS shocks.
• The government can increase spending to
counteract shocks in the short run.
– Increases in government spending produce higher
prices in the long run.
Summary