1. Macroeconomics
Unit 9
Aggregate Demand

2. Introduction
In this unit we examine the components of aggregate demand closely. One of the key components is consumer consumption.
Economists know that consumer consumption is dependent upon the amount of income they receive; but some consumption is not determined by current income.
Business investment, government spending, and net exports are also explored in this unit.

3. Aggregate Demand
Aggregate demand (AD) is the total quantity of output (GDP) demanded at alternative price levels in a given period, ceteris paribus.
AD consists of four components:
Consumption (C)
Investment (I)
Government Spending (G)
Net Exports (X – IM)

4. Concept 1: Consumption
Consumption represents purchases by consumers on final goods and services. Consumption is obtained from consumer disposable income.
Disposable income must be either spent or saved. Therefore the following formula applies:
Disposable Income (YD) = Consumption (C) + Saving (S)

5. Concept 1: Consumption
We often want to determine the proportion of total disposable income spent on consumer goods and services.
The average propensity to consume (APC) is equal to total consumption on consumer goods and services in a given time period divided by total disposable income.
APC = total consumption / total disposable income =
C / YD

6. Concept 1: Consumption
In 1999, total consumer consumption totaled $6,490 billion, and total disposable income was $6,638 billion. Therefore the APC =
$6,490 billion /$6,638 billion = .98
98 cents out of each dollar earned was spent on consumption in In 2001 the U.S. APC was indicating that consumers actually spent more than they received from income.

7. Concept 1: Consumption
Often we would like to know what consumers would do if they received a change in their disposable income.
To determine this change, we calculate the marginal propensity to consume (MPC).
The marginal propensity to consume is the fraction of each additional dollar of disposable income spent on consumption. It is calculated by taking the change in consumption and dividing it by the change in disposable income.

8. Concept 1: Consumption MPC = ΔC / ΔYD
To calculate MPC we need to know how consumers spend the last dollar they receive.
If consumers spend 80 cents out of the last dollar, then MPC = $0.80/$1.00 = .80.
Notice that the MPC is lower than the APC we previously calculated. Consumers tend to save a greater percentage of the last dollars earned.

9. Concept 1: Consumption
We are also concerned with how much consumers save from each additional dollar they earn.
The marginal propensity to save (MPS) is the fraction of each additional dollar of disposable income not spent on consumption.
MPS = ΔS / ΔYD or MPS = 1 – MPC
If consumers save $0.20 out of the last dollar earned, what is the MPS? The MPS = .20/1.00 = .20.

10. Concept 1: Consumption
We are also concerned with the average rate of consumer saving. To determine this, we calculate the average propensity to save (APS).
The APS = S / YD or APS = 1 – APC
Suppose disposable income is $6,698 billion and consumers saved $208 billion. What is the APS? The APS = $208 billion/$6,698 billion = Consumers save an average of $0.031 out of each dollar of disposable income.

11. Concept 1: Consumption
Although calculating the MPC, MPS, APC, and APS is useful, predicting them is even more important. What drives consumer consumption?
Keynes believed that consumer consumption was driven be current income and other non-income determinants.
The non-income determinants of consumption according to Keynes are: expectations, wealth, credit, taxes, and price levels. Consumption based upon one or more of these determinants is called autonomous consumption.

12. Consumption Concept 2: Non-Income Determinants
Expectations is concerned with consumers changing current consumption based upon an anticipated future event.
Consumers will spend a portion of anticipated salary increases, tax refunds, bonuses, often before they are received. If this is occurring, autonomous consumption increases.
If consumers believe they may get their work hours cut, laid off, or have their jobs eliminated, they will spend less and save more. Autonomous consumption declines.

13. Consumption Concept 2: Non-Income Determinants
Wealth is the amount of assets an individual owns. This can affect their consumption.
Increases in wealth create greater spending of current income. Autonomous consumption increases.
Decreases in wealth causes spending of current income to decline. Autonomous consumption declines.

14. Consumption Concept 2: Non-Income Determinants
Credit is the amount and availability of credit. It also can affect consumption.
If credit is readily available, consumer spending of current income increases causing an increase in autonomous consumption.
If credit is not easily attainable or costly (high rates), consumer spending of current income decreases and autonomous consumption declines.

15. Consumption Concept 2: Non-Income Determinants
Taxes are another non-income determinant. Decreases in taxes increase consumer disposable income and consumer spending. This would cause an increase in autonomous consumption. Tax increases reduce consumer disposable income and consumer spending, causing a decline in autonomous consumption.
Price-levels are the final non-income determinant. If price levels are increasing (inflation), the real value of money is reduced, and consumer spending is reduced by the effects of inflation. Autonomous consumption is reduced.

16. Consumption and the Concept 3: Consumption Function
We have learned that consumer spending is influenced by current income, and the non-income determinants of consumption.
Therefore total consumption = non-income determinants of consumption + income-dependent consumption, or total consumption = autonomous consumption + income-dependent consumption. The formula that represents this relationship is:
C = a + bYD

17. Consumption and the Concept 3: Consumption Function
The equation C = a + bYD represents the consumption function.
The consumption function is a mathematical relationship indicating the desired consumer spending at various income levels.
C = current consumption
a = autonomous consumption
b = marginal propensity to consume
YD = disposable income

18. Consumption and the Concept 3: Consumption Function
The consumption function is used to predict how changes in disposable income (YD) will affect consumer spending. It also shows the effect of changes in one or more non-income determinants (autonomous consumption) on consumer spending.
A consumption function can be graphically illustrated to show the relationship between consumption and disposable income.

19. Concept 3: A Consumption Function
C = YD
Saving
Consumption Spending
Dissaving
Disposable Income
A graph of the consumption function line and the 45 degree line representing the points at which consumption = income. The graph shows areas of dissaving below where the two line intersect and savings above.

20. Concept 3: A Consumption Function
The graph on the preceding page illustrates a consumption function. The green dotted line represents the points at which consumption is equal to disposable income – no saving or dissaving occurs. This is called the 45 degree line representing C = YD.
The red solid line represents the actual consumption. Whenever the red line is below the green line savings occurs. Once you reach the point at which the two lines intersect, any additional spending is more than disposable income and dissaving occurs (the green dotted line is below the red line of the consumption function).

21. Concept 3: Consumption and the Consumption Function
To graph the consumption function for a individual or for an economy, we need to know the level of autonomous consumption, the MPC, and the amount of disposable income.
If autonomous consumption = $100, and the MPC = .50, then our equation is:
C = $ YD
Once we know different levels of disposable income, we can graphically represent the consumption function.

22. Fred’s Consumption Function
A table showing a sample consumption function for Fred.

23. Fred’s Consumption Function
$400
C = YD
300 E
Saving C D
200
Dissaving B
Consumption Function
C = $ YD A
100
$50
100
150
200
250
300
350
400
450
A graph of a sample consumption function for Fred showing areas of dissaving and saving depending upon the level of income.

24. Concept 3: Consumption and the Consumption Function
A graph of a consumption function will contain a 45 degree line which represents the point at which consumption (C) = disposable income (YD). On the preceding graph, this line is the green dotted line at a 45 degree angle.
Actual consumption may be above this line (dissaving) or below the line (saving). Actual consumption is represented by the consumption function equation and line. This line is shown as the solid red line on the preceding graph.
The slope of the consumption function line will always equal the MPC.

25. Concept 3: Consumption and the Consumption Function
At point A, Fred has autonomous consumption of $100 and no income. At point B Fred now has $100 in income, $100 in autonomous consumption, and $50 in income dependent consumption. Fred continues to dissave.
The consumption function equation determines the dollar amount of Fred’s income dependent spending. Since Fred’s MPC = .50, Fred will spend half of his income.
At point C, Fred’s income finally equals his autonomous and income dependent consumption. At points D and E, Fred’s income exceeds his total spending and he is saving.

26. Aggregate Consumption Function
The aggregate model of the consumption function is essentially identical to the simple consumer model presented.
Shifts of the consumption function can occur when a change occurs in one of the autonomous consumption determinants (expectations, wealth, credit, taxes, price levels). For example, significant positive returns in the stock market can increase consumer wealth which would cause autonomous consumption to increase. This would cause the consumption function to shift upwards.

27. Shift in the Consumption Function
CONSUMPTION (C) (dollars per year)
DISPOSABLE INCOME(dollars per year)
Increased confidence
Greater wealth
A graph showing a upward shift in the consumption function caused by an increase in consumer confidence or greater wealth.

28. Movement along the Consumption Function
Movement along the consumption function occurs when there is a change in income or a change in the MPC.
A decline in income causes a leftward movement along the consumption function (from point A to B on the next slide).
A decline in MPC also causes a leftward movement along the consumption function.

29. Movements along the Consumption FunctionB
Movement along the curve
(billions of dollars per year)
CONSUMPTION
A graph showing movement along the consumption function to the left. Movement occurs when there is a change in income or the MPC.
DISPOSABLE INCOME (billions of dollars per year)

30. Consumption Function
You should notice that when the consumption function shifts, there is a change in autonomous consumption. Overall consumption has changed as a result of a change in non-income dependent consumption.
The point at which the line representing the consumption function intersects the Y axis changes when autonomous consumption changes.
When the line shifts up it indicates an increase in autonomous or non-income dependent consumption. When the line shifts down it indicates a decrease in autonomous or non-income dependent consumption.

31. Consumption Function
When there is movement along the consumption function, the level of autonomous consumption does not change.
Overall consumption has changed as a result of a change in income-dependent consumption.
Movement along the consumption function line indicates a change in income. Movement to the right occurs when income increases and movement to the left occurs when income decreases.

32. Consumption and AD
The consumption function and aggregate demand curves will move together.
A downward shift of the consumption function implies a leftward shift of the AD curve. Demand/consumption have fallen.
An upward shift of the consumption function implies a rightward shift of the AD curve. Demand/consumption have risen.

33. AD Effects of Consumption Shifts
AD shifts to the right
indicating increased output
Spending
Income
Price Level AD AD
Consumption function shifts up indicating an increase in autonomous consumption
Real Output
Two graphs showing the relationship between an upward shift in the consumption function and a rightward shift in aggregate demand.

34. Concept 4: Investment
A change in consumer spending is not the only factor that affects aggregate demand.
The other factors (investment, government services, and net exports) can offset changes in consumer spending.
Investment accounts for about 18% of output and consists of expenditures on new plant, equipment, business software, inventory, new residential construction.
There are also determinants of investment.

35. Concept 4: Determinants of Investment
Expectations – The expectations of business owners and management for future growth and sales of their products. Future sales, future economic factors, future trends.
Interest Rates – The current and expected rates of interest for loans. Businesses need to borrow to expand – if rates are low this is favorable. At higher rates of interest business investment declines.

36. Concept 4: Determinants of Investment
Technology and Innovation – The impact of improved technology and innovation on the ability to manufacture goods at a lower cost. Improving technology can improve profits and increase investment in other improvements.

37. Concept 4: Determinants of Investment
A change in any of the determinants of investment will cause a shift in the investment function (investment demand curve). For example, if factor costs increase, the investment demand curve will shift to the left. If improved economic conditions are expected, the investment demand curve will shift to the right.
If investment spending declines, the aggregate demand curve will shift to the left. As investment spending increases, the aggregate demand curve shifts to the right. Historically there have been wide swings in the amount of investment spending; it is much more volatile than consumer spending.

38. Investment Demand And Interest Rates
Better expectations cause a shift rightward 11
Interest Rate (percent per year)
Planned Investment Spending (billions of dollars per year)
100
200
300
400
500 10 9 8 7 6 5 4 3 2 1 11
Movement up the existing curve
is caused by an increase in interest rates I2
Initial expectations
Worse expectations -
The curve shifts left I3

39. Government Spending
The level of government spending can have an impact on aggregate demand.
Increases in government spending can shift the aggregate demand curve to the right.
Federal government spending is less dependent upon tax collections. Deficit spending is often used to supplement spending programs.

40. Net Exports
Exports depend upon the needs and demand of foreign consumers and businesses.
Economic factors affecting other countries affect the amount of exports we can sell. Declines in exports cause a leftward shift of the AD curve.
Strong demands for imported goods can be weakened by a drop in consumer confidence. If imports are preferred over domestically produced items aggregate demand can shift to the left.

41. Concept 5: Macro Failure
When the economy is at the equilibrium price and quantity, the economy may not be at its optimal level of output.
According to Keynes at equilibrium we may not be at a full employment level of output and price stability may not exist.
Even if the equilibrium point gives us full employment and price stability, it will likely change.

42. Concept 5: AD & AS at Full Employment
Macro Success: (perfect AD)
QF indicates output at full employment
Price Level
Real GDP AS
AD1 E1 P* QF
A graph showing AD and AS with equilibrium at full employment.

43. Concept 5: Insufficient AD - Unemployment
The GDP gap
Equilibrium is below full employment output
Price Level
Real GDP AS
AD2 F2 P* Q2 QF P2
QE2 E2
recessionary GDP gap
A graph with AD and AS intersecting at E below the level of output necessary for full employment. This causes a recessionary GDP gap.

44. Concept 5: Macro Failure
Recessionary GDP Gap – The amount of which equilibrium GDP (QE) falls short of full-employment GDP (QF). This is defined as a macro economic failure.
Graphically, the distance between the quantity produced at full employment and the quantity at which AD and AS intersect (see the previous graph – the distance between QE and QF.
Full employment GDP – The value of total output (real GDP) produced at full employment. Full employment GDP is the major goal of economic policy.

45. Concept 5: Too Much AD Inflationary gap exists between QF and QE3
Demand-pull inflation: (too much AD)
Equilibrium is above full employment output
Price
Level AS
AD3 P3 E3
QE3 P* QF Q3
Inflationary GDP gap
Real GDP
A graph of AD and AS showing the intersection at E above the level of full employment output. This causes an inflationary gap and higher prices.

46. Concept 5: Macro Failure
Inflationary GDP Gap – The amount by which equilibrium GDP exceeds full employment GDP. Graphically, the distance between full employment GDP and the intersection of AD and AS. In the preceding graph, the distance between QF and QE.
Therefore, if AD is too high or too low the economy will not reach its goals of full employment and price stability. The recessionary or inflationary gaps must be closed by using economic policies to increase or decrease AD and/or AS.

47. Concept 5: Macro Failure
How do you tell from a graph what kind of a gap exists?
Look first for the quantity associated where AD and AS meet. This point is often referred to as QE.
Look for the designated point for full employment output, usually labeled QF.
Is QF above QE? If yes, you have a recessionary GDP gap. If no, you have an inflationary GDP gap. If QF represents the point at which AD and AS intersect, you are at full employment at macro equilibrium.

48. Too little, too much, just right
QR represents output during a recessionary gap while QI represents output during an inflationary gap. QF is the output level at full employment.
Price Level
Real GDP AS QI P* QF QR
A graph showing three different demand curves depicting a recessionary gap, full employment output, and an inflationary gap.

49. Summary Components of AD. APC, APS, MPC, MPS. Autonomous consumption.
Non-income determinants of autonomous consumption (5).
Income dependent consumption.
Consumption function – C = a + bYD
45 degree line.
Dissaving.
Shifts in the consumption function.
Shifts in AD.

50. Summary Investment and AD. Determinants of Investment (3).
Causes of investment shifts.
Macro failure.
Graphs of full employment GDP, equilibrium GDP, recessionary GDP gap, inflationary GDP gap.