The document discusses key concepts related to consumption functions, including: 1) Consumption depends mainly on current income but is also influenced by other factors like interest rates and wealth. As income rises, consumption increases at a lower rate due to savings. 2) Average Propensity to Consume (APC) and Marginal Propensity to Consume (MPC) measure the relationship between consumption and income. APC is the ratio of total consumption to total income, while MPC is the change in consumption over a change in income. 3) Effective demand, the combination of consumption and investment demand, must remain high to maintain employment levels. Investment demand depends on the marginal efficiency of capital (MEC).

1. Consumption Function

2. Consumption Function
 Theory of consumption function explain relationship
between consumption & income
 As per J.M Keynes, consumption expenditure of household
depends mainly on their current income
 Other factors influence like interest rate, taxation, amount of
wealth etc.
 As per Keynes, when income increases, consumption
increases but in a lesser proportion due to savings factor
 Consumption Function is also known as Propensity to
consume

3. APC & MPC
 Consumption function can be explained through Average
Propensity to Consume (APC) and Marginal Propensity to
Consume (MPC)
 APC – ratio of total consumption expenditure to total
income
 APC = C / Y i.e. Consumption / Income
 For instance, C = 60,000, Y = 1,00,000
 APC = 60000 / 1,00,000 = 0.6 or 60%
 Household spends 60% of its income on consumption

4. APC & MPC
 MPC – Ratio of change in consumption to change in
income
 MPC = C / Y i.e. Change in Consumption / Change
in Income
 Instance, change in C = 60,000 to 1,00,000 & Y =
1,00,000 to 2,00,000
 MPC = 40,000 / 1,00,000 = 0.4 or 40%

5. APS & MPS
 Counterparts of APC & MPC are APS & MPS
 APS – Average Propensity to Save
 MPS – Marginal Propensity to Save
 APS = S / Y (S = Savings, Y = Income)
 MPS = S / Y (Change in Savings / Change in Income)
 APC +APS = 1 and MPC + MPS = 1
 Rich people have more of MPS compared to poor
 MPC will be greater than MPS

6. Y C APC (C/Y)
APS
(S/Y)
(1 – APC)
MPC
( C/ Y)
MPS
( S/ Y)
(1-MPC)
1000 1000 1 0 - -
2000 1800
1800/2000
= 0.9
0.1
800/1000
= 0.8
0.2
3000 2500
2500/3000
= 0.83
0.17
700/1000
= 0.7
0.3
4000 3000
3000/4000
= 0.75
0.25
500/1000
= 0.5
0.5
5000 3200
3200/5000
= 0.64
0.36
200/1000
= 0.2
0.8

7. Factors Determining Consumption
Function
 2 types of Factors
 Objective Factors
 Subjective Factors – help in more saving rather than
spending hence consumption is reduced

8. Objective Factors
 Size of Income
 Price Level
 Distribution of Income
 Propensity to Save
 Future Expectations
 Taste & Fashion
 Rate of Interest
 Sudden Gains or Losses
 Ownership of Assets
 Corporate Policy (Dividend)
 Fiscal Policy
 Other Factors (Loans)

9. Subjective Factors
 Precaution against illness, accident, unemployment etc.
 Future Expectations & Needs
 Accumulation of Wealth
 Independence
 Investment
 Speculation

10. Marginal Efficiency of Capital

11. Effective Demand
 J.M. Keynes emphasises on high level of effective
demand to maintain high level of employment
 Effective Dem = Consumption Dem + Investment Dem
 Consumption Demand
 Demand for final goods & services
 Depends upon level of income & propensity to spend
 In Short run, it remains stable

12. Effective Demand
 Investment Demand
 Demand for Capital Goods
 Depends upon rate of interest and marginal efficiency of
capital
 In short run, rate of interest is stable
 Marginal Efficiency of Capital is influential factor in
determining level of investment demand
 In short run, consumption demand remains stable hence,
level of employment is influenced by investment demand

13. Marginal Efficiency of Capital
(MEC)
 MEC is the expected rate of profitability from a capital asset
 Rate of Return expected over & above the cost of an
additional unit of capital asset
 Capital Asset is brand new asset & not existing one
 Similarly, “return” is expected returns & not existing returns
or actual returns
 MEC depend upon prospective yield from capital asset &
supply price of the asset

14. Marginal Efficiency of Capital
(MEC)
Prospective Yield From Capital
Asset
Supply Price of
Capital Asset
 Total net return expected
from asset over its lifetime
 Net income received by
selling its output
(products manufactured
by machinery)
 Net Income = Gross
Income – Cost
 Price of asset is considered
before purchasing
 Comparison is made
between supply price &
yield from the asset
 Investment is made when
yield is more than supply
price

15. MEC
 According Keynes, MEC is the rate at which prospective yield
from a new capital asset to be discounted to make it equal to the
supply price of the asset
 Supply Price = 10,000 , Prospective Yield = 15,000
 MEC = Price gap between them
 Formula to equalize prospective yield to supply price
 Cr = Q1/(1+r)1 + Q2/(1+r)2 + Q3/(1+r)3 ...... Qn/(1+r)n
 Cr = Supply Price of asset, Q1, Q2 = annual returns from capital
asset, r = rate of discount (marginal efficiency of capital)

16. MEC
 To find out r, formula can be rearranged as
 r = Q1 - 1
Cr
 For Instance, Supply Price = 1000 crore, Prospective yield for 1st
year = 1250 crore
 r or MEC = 1250 / 1000 -1 = 0.25 or 25%
 When MEC is known and Prospective yield is to be calculated
 Cr = Q1 1000 = Q1 = 1250
(1+r)1 1+0.25
 MEC and Interest Rate is compared, if MEC > Interest rate, then
investment project will be undertaken

17. Investment Demand Curve
 MEC curve slopes
downwards from left to
right indicating inverse
relationship between
Investment & MEC
 When more investment is
made, prospective yield
will decline supply price
will rise

18. Questions
1. Explain the concept of consumption function
2. Differentiate between APC & MPC, APS & MPS
3. Throw light on the factors influencing consumption
function (Subjective or objective can come as short Note)
4. Sums to Calculate APC, MPC, APS, MPS will come
5. Discuss the concept of Effective Demand
6. Throw light on the concept of MEC with suitable diagram
7. Explain Investment Demand Curve
8. Sums to calculate MEC, Cr, Q will come