# ECO102H1 Lecture Notes - National Income And Product Accounts, Disposable And Discretionary Income, Consumption Function

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**preview**shows pages 1-2. to view the full**8 pages of the document.**Chapter 21: The simplest short run Macroeconomics

21.1 Desired aggregate expenditure

The national accounts divide actual GDP into its components: - Ca, Ia , Ga, and NXa.

Total desired expenditure is divided into the same categories:

• desired consumption, C

• desired investment, I

• desired government purchases, G

• desired net exports, NX

Desired aggregate expenditure (AE): the sum of desired or planned spending of domestic by households, firms,

government, and foreigner.

The sum is called desired aggregate expenditure: AE = C + I + G + NX

Desired expenditure need not equal actual expenditure, either in total or in any individual category. Sometimes

in cases actual expenditure can exceed the desired expenditure.

National income accounts measure actual expenditures in each of the four expenditure categories. National

income theory deals with desired expenditure in each of these four categories.

Two types of expenditures:

Autonomous vs. Induced expenditure:

Autonomous expenditure: elements of expenditure that do not change systematically with national income.

Autonomous expenditure can and do a change , but such changes do not occur systematically in response to

changes in national income.

Induced expenditure: any component of expenditure that is systematically and related to national income

Important simplifications:

In order to develop the simplest possible model of national income determination, this chapter will focus on

only consumption and investment, which is two of four components of desired aggregate expenditure

Closed economy: economy that has no foreign trade in goods and services or assets.

A close economy also had no government and that the price level is constant.

Desired consumption expenditure

Disposable income is the amount of income households receive after deducting what they pay in taxes and

adding what they have received in transfer

Two possible uses of disposable income: - consumption (C) or saving (S)

In the simplest theory, consumption is determined primarily by current disposable income (YD) which equals to

national income, Y.

Saving: all disposable income that is not spent on the consumption

By definition, there are only two possible uses of disposable income—consumption and saving. When the

household and decides how much to put to one use, it has automatic team decided how much to put to the

other use.

The graph below shows the time series for real per capita consumption and disposable income in Canada. It is

clear that the two variables tend to move together over time, although the relationship is not exact. The vertical

distance between the two a lines is the amount of saving down by households

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Factors that influence what determines the amount of disposable income that households decide to consume

and save is consumption function and the saving function

The consumption function: the relationship between into side consumption expenditure and all the variables

that determine it; and the simplest case, the relationship between inside consumption expenditure and

disposable income.

The key factors influencing desired consumption are assumed to be: disposable income, wealth, interest rates,

and expectations about the future.

Holding constant other and determinates of desired consumption, an increase in disposable income is

assumed to lead an increase in a desired consumption

Desired consumption is positively related to current disposable income is a good approximation of the behavior

of the average household and therefore is suitable for explaining and aggregate behaviour

The simple consumption function is written as: C = a + bYD

The graph above (i) illustrates a hypothetical consumption function.

The first graph is showing a positive relationship between desired consumption C associated with each value of

disposable income Yd. The figure plots these points and connects them with the smooth line. In this hypothetical

economy, the equation of consumption function is: C= 30 + 0.8 Yd. In other words this equation says that in

disposable income is zero, desired aggregate consumption will be 30 billion and that every $1.00 increase in Yd,

decide consumption rises by 80¢.The 30 billion is said to be autonomous consumption because it is autonomous

of level of income. The 0.8Yd is called in Yd as consumption because it is induced by a change in income.

Autonomous part of desired consumption is the vertical intercept of the consumption function in the first graphs.

The induced part of consumption occurs as disposable income changes as we move along the consumption

function (line C).

The second graph shows the relationship between decides saving and disposable income. Line S which plots the

data about desired saving (S) . The vertical distance between C and 45 degree line in first graph is by definition

the height of line S graphs that is that any level of disposable income must be either consumed for saved.

Average and marginal propensities to consume:

Average propensity to consume (APC): designed consumption divided by the level of disposable income. APC =

C/Yd

Average propensity to consume falls as disposable income rises

Marginal propensity to consume (MPC): the change in desired consumption divided by the change in disposable

income that brought it about. MPC= delta C/ Delta Yd

MPC will always equal to the slope of desired consumption expenditure line

The slope of the consumption function:

The consumption function’ slope is the marginal propensity to consume. The positive slope of the consumption

function shows that the MPC is positive increase in income lead to increase in desires consumption expenditure.

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The constant slope of the consumption function shows that the MPC is the same at any level of disposable

income.

The 45 degree line:

The line and constructed by connecting all the points where desired consumption (vertical axis) equals to

disposable income (horizontal axis). Because both axes are given in the same units, this line has a positive slope

equal to 1 that is it forms an angle of 45 degree with the axes called the 45 degree line

When the consumption function cuts the 45 degree line at what is called the “break-even” level of income.

When the consumption function is about the 45 degree line, desired consumption exceeds disposable income.

In this case, decide saving must be negative; households are financing their consumption either by spending out

of their accumulated saving or by borrowing funds.

When the consumption function is above the 45° line, decide consumption is less than disposable income and so

desires saving is positive; households are paying back debt or it’s accumulating assets.

At the break-even level of disposable income, designed consumption eggs that the aequals disposable income

and so desired saving is zero.

The saving function:

Once we know relationship between desired consumption and disposable income, we automatically know the

relationship between a desired saving and disposable income.

There are 20 saving concepts that are exactly parallel to the consumption concepts:

Average propensity to save (APS): the desired saving divided by disposable income. APC = S/Yd

Marginal propensity to save: the change in desired saving divided by the change in disposable income that

bought is about. MPS = delta S/ Delta Yd

There is a single relationship between the saving and consumption propensities. APS and APC must sum to 1.

And MPC and MPS must also sum to 1. Because all disposable income is either spend or save, it follows that the

fraction but of income consumed and save must account for all income, ( APC +APS = 1)

It also follows that the fractions of any increment to income consumed and saved must act called for all of that

increment. (MPC +MPS =1)

Increase in disposable income is assumed to lead to an increase in desired saving. If the mother desire saving all

is equal to the vertical distance between the consumption function and a 45 degree line.

And when consumption exceeds income desired saving is negative, when desired consumption is less than

income desired saving is positive

Shift in the consumption function:

Changes in disposable income lead to movements along the consumption function.

Changed in the other three factors will lead to shift of the consumption functions.

A change in household wealth:

Household wealth is the value of all its accumulated assets minus accumulated debts.

An increase in household wealth shifts the con consumption function up, a decrease In wealth shifts the

consumption function down.

A change in interest rates:

Households consumption can be divided into consumption of durable and nondurable goods

Durable goods are goods that deliver benefits for several years, such as car and household appliances. And

nondurable goods are consumption goods that deliver benefits to households for only a short period of time

such as groceries, restaurant meals and clothing.

A fall in interest rates usually needs to an increase in desired consumption at any level of disposable income,

the consumption function shifts up. A rise in interest rates shares the consumption function down.

A change in expectations:

Expectations about the future state of the economy influence as desired consumption. Optimism leads to an

output shift in the consumption function; pessimism leads to a downward shift in the consumption function.

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