The aggregate demand supply model
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THE AGGREGATE DEMAND/ SUPPLY MODEL. The U.S. Great Depression. 1929-1939 Output fell by 30% Unemployment as high as 25% Prices declined 30% in the first four years Led to the development of modern macroeconomic theory Video. Before: Classical Economics.

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THE AGGREGATE DEMAND/ SUPPLY MODEL

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The aggregate demand supply model

THE AGGREGATE DEMAND/ SUPPLY MODEL


The u s great depression

The U.S. Great Depression

  • 1929-1939

    • Output fell by 30%

    • Unemployment as high as 25%

    • Prices declined 30% in the first four years

  • Led to the development of modern macroeconomic theory

    Video


Before classical economics

Before: Classical Economics

  • Focused on long-run issues--growth

  • Self-regulating markets through the “invisible hand”

    • Prices would adjust during recessions

    • Economy would always return to its potential output in the long-run

  • Depression caused by institutions that prevented prices from falling, specifically:

    • Labor unions

    • Government

  • Advocated a laissez-faire (hands-off) economic policy


After keynesian economics

After: Keynesian Economics

  • John Maynard Keynes in The General Theory of Employment, Interest, and Money (1936)

  • Problems of the Depression required a short-run, rather than long-run, focus.


Keynesian economics

Keynesian Economics

  • Adjustments to equilibrium for a single market and the aggregate economy are different.

  • Short-run equilibrium income may differ from long-run potential income.

  • Paradox of thrift

    • In long run, saving leads to investment and growth.

    • In short run, saving may lead to a decrease in spending, output, and employment.

  • Aggregate demand management by government may be necessary.


Keynesian economics and the as ad model

Keynesian Economics and the AS/AD Model

  • Aggregate Demand Curve (AD)

    • Relates changes in the price level to changes in aggregate expenditures =

      C + I + G + (X-M)

  • Short-Run Aggregate Supply Curve (SAS)

    • Relates changes in the price level to changes in aggregate supply.

  • Long-Run Aggregate Supply Curve (LAS)

    • Shows potential output at any point in time


The aggregate demand curve

Multiplier effect

The Aggregate Demand Curve

Price

level

Wealth, interest rate, and international effects

P0

P1

AD

Y0

Y1

Ye

Real output


Shifts in the ad curve

200

100

AD1

Shifts in the AD Curve

Initial effect = 100 increase in expenditures

Price level

Multiplier effect = 200

Change in total expenditures = 300

P0

AD0

Real output


The short run aggregate supply curve

The Short-Run Aggregate Supply Curve

SAS

Price level

Real output


Shifts in the sas curve

Shifts in the SAS Curve

1. Higher input prices

SAS1

2.Higher import prices

3. Higher sales and excise

taxes

Price level

4. Reduced productivity

SAS0

Real output


Long run aggregate supply curve

LAS1

Long-Run Aggregate Supply Curve

LAS

  • LAS curve shows potential output

  • Vertical because potential output

  • is unaffected by the price level.

Price Level

  • Increases in capital, resources,

  • growth-compatible institutions,

  • technology, and entrepreneur-

  • ship increase potential output

  • and shift LAS to the right.

Potential

output

Real output


Las curve

LAS Curve

LAS

  • Potential output is assumed to be the

  • middle of a range bounded by high

  • and low levels of potential output.

C

  • When resources are over-utilized

  • (point C), factor prices may be bid

  • up

  • When resources are under-utilized

  • (point A), factor prices may be bid

  • down

B

A

SAS

Price Level

Underutilized

resources

Overutilized

resources

  • When LAS = SAS (point B), there is

  • no pressure for prices to rise or fall.

Real

output

Low-level potential output

High-level potential output


Short run equilibrium changes in ad

P1

F

P0

E

AD1

AD0

Y1

Y0

Short-Run Equilibrium:Changes in AD

  • Short-run equilibrium is

  • where SAS = AD0 (point

  • E).

Price level

  • If AD increases to AD1,

  • equilibrium output

  • increases to Y1 and the

  • price level increases to P1.

SAS

P0

E

AD0

Y0

Real output


Short run equilibrium changes in sas

SAS1

G

P1

E

P0

Y1

Short-Run Equilibrium:Changes in SAS

  • Short-run equilibrium is

  • where SAS0 = AD (point

  • E). Equilibrium output is

  • Y0 and the price level is

  • P0.

Price level

SAS0

  • If SAS increases to SAS1,

  • equilibrium output

  • decreases to Y1 and the

  • price level increases to P1

  • (point G).

E

P0

AD

Y0

Real output


Long run equilibrium

H

P1

AD1

Long-Run Equilibrium

LAS

Price level

  • Long-run equilibrium is

  • point E where AD0 = LAS.

  • Equilibrium output is at

  • potential output YP and

  • the price level is Po.

E

P0

  • An increase in AD to AD1

  • increases the price level

  • to P1 but output is un-

  • changed at YP.

AD0

YP

Real output


Integrating short run and long run frameworks

Integrating Short-Run and Long-Run Frameworks

  • The economy is in long-run and short-run equilibrium at point E where AD=SAS=LAS and output is YP and the price level is P0.

LAS

SAS

E

Price level

  • AD grows at the same rate as potential output, so that unemployment and inflation are very low.

P0

AD

YP

Real output


Recessionary gap

SAS0

A

P0

Y1

Recessionary Gap

  • A recessionary gap is the amount by which equilibrium output is below potential output.

LAS

  • At point A, some resources are unemployed and the recessionary gap is YP – Y1.

SAS0

A

P0

Price level

AD

Recessionary

gap

Y1

YP

Real output


Inflationary gap

Inflationary Gap

  • An inflationary gap is the amount by which equilibrium output is above potential output.

LAS

Price level

  • If the economy is at point C, resources are being used beyond their potential and the inflationary gap is Y2 – YP.

C

SAS0

P0

AD

Inflationary

gap

YP

Real

output

Y2


Expansionary fiscal policy

B

P1

AD1

YP

Expansionary Fiscal Policy

Price level

  • Economy is at equilibrium at A, there is a recessionary gap Y0 – YP.

LAS

  • Appropriate fiscal policy is to increase government spending and/or decrease taxes.

SAS

P0

A

A

  • AD increases to AD1 and output returns to potential output YP and prices increase slightly to P1.

AD0

Y0

Real output


Contractionary fiscal policy

AD2

Contractionary Fiscal Policy

LAS

  • Economy is at equilibrium at B, there is an inflationary gap Y2 – YP.

  • Appropriate fiscal policy is to decrease government spending and/or increase taxes.

B

AS

P2

Price level

AD0

  • AD0 decreases to AD2 and output returns to potential output YP and inflation is prevented.

YP

Y2

Real output


Macro policy problems

Macro Policy Problems

  • Implementing fiscal policy

    • Slow legislative process

    • Slow and uncertain reaction by the economy

  • Avoiding “over-correcting”


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