2. THEORY OF CONSUMER BEHAVIOUR
CHAPTER 4
THEORY OF CONSUMER BEHAVIOUR

3. DEFINITION OF CONSUMER BEHAVIOUR
Consumer behaviour refers to
the study of consumer while engaged in the process of consumption.

4. UTILITY APPROACH Definition
‘Utility’ means the satisfaction obtained from consuming a commodity.
Two Types of Approach
Cardinal Approach
The cardinal utility theory says that utility is measurable and by placing a number of alternatives so that the utility can be added.
The index used to measure utility is called utils.
Ordinal Approach
The ordinal utility theory says that utility is not measurable but it can be compared.
Ordinal approach uses the ranking of alternatives as first, second, third and so on.

5. TOTAL UTILITY AND MARGINAL UTILITY
TOTAL UTILITY (TU)
The total satisfaction that a person gets from the
consumption of goods and service.
TOTAL UTILITY AND MARGINAL UTILITY
MARGINAL UTILITY (MU)
The additional to total utility as a result of consuming one more units
of the same good or services.
Marginal Utility (MU) = Change in Total Utility
Change in Total Quantity
MU =  TU/  Q

6. LAW OF DIMINISHING MARGINAL UTILITY
Definition
The additional benefit which a person derives from a given increase of a stock decreases with every increase in the stock that he already has. OR
Law of Diminishing Marginal Utility states that as consumption increases more and more, marginal utility will be less and less.

7. LAW OF DIMINISHING MARGINAL UTILITY (cont.)
TU increases from consumption of 1st unit of apple until the 5th unit of apples. After the 5th unit of apples, TU will decrease.
Units of Apples
Total Utility
Marginal Utility 1 20 2 35 15 3 45 10 4 50 5 6 -5 7
-10 8
-15
MU will decrease and become zero at the 5th unit of apples and further consumption of apples will not satisfy the consumer as the MU shows negative signs.

8. LAW OF DIMINISHING MARGINAL UTILITY (cont.)
When TU is increasing, MU will be positive.
When TU is at its maximum, MU will be zero.
When TU is decreasing, MU will be negative.

9. LAW OF EQUI-MARGINAL UTILITY (EMU)
Definition
The Law of Equi-Marginal Utility (EMU) states that other things being equal, a consumer gets maximum satisfaction when he allocates his limited income to the purchase of different goods, where the marginal utility derived from the last unit of money spent on each item of expenditure tends to be equal.
This is also known as conditions for maximum utility or satisfaction.

10. LAW OF EQUI-MARGINAL UTILITY (EMU) (cont.)
Conditions for Equilibrium
For consumer equilibrium, this condition must be fulfilled.
Condition 1: Every ringgit spent on every commodity must yield the same marginal utility.
Marginal Utility of X = Marginal Utility of Y
Price of X Price of Y
Condition 2: Total expenditure of all goods must be equal to the total budget allocated to maximize utility.
P1Q1 + P2Q2 + … + PnQn = Total budget

11. LAW OF EQUI-MARGINAL UTILITY (EMU) (cont.)
EXAMPLE: Arwin has an income of RM37 and the prices of goods P, Q and R are RM5, RM1 and RM4 respectively.
Condition 1 : Every ringgit spent on every commodity must yield the same marginal utility.
Fulfilling condition 1, two combination of goods are obtained:
Combination 1 : 2P, 4Q and 1R
Combination 2 : 4P, 5Q and 3R
Quantity
Product P
Product Q
Product R
Total Utility
MUP/PP
MUQ/PQ
MUR/PR 1 21
4.2 7 16 4 2 41 13 6 30
3.5 3 59
3.6 18 5 42 74 22 50 85
2.2 25 55
1.25 91
1.2 27 58
0.75 28 60
0.5
Combination 1 : 2P, 4Q and 1R
2(5) + 4(1) + 1(4) = 18
Combination 2 : 4P, 5Q and 3R
4(5) + 5(1) + 3(4) = 37
So, 4 units of Product P, 5 units of Product Q and 3 units of Product R will be purchased by Arwin.
Condition 2 : Total expenditure of all goods must be equal to the total budget allocated to maximize utility.

12. INDIFFERENCE CURVE Definition Assumptions
An indifference curve represents all the possible combinations of two goods which will give the same level of satisfaction.
Assumptions
Scale of preferences
Consumers’ preferences are transitivity
Rationality
Diminishing marginal rate of substitution
Concept of ordinal utility

13. INDIFFERENCE CURVE (cont.)
An indifference schedule is a list of combination of two goods that give equal satisfaction to the consumer.
Combinations
Good Y
Good X A 12 2 B 6 4 C D 3 8 E
The table above shows all the five combinations, which will give the equal level of satisfaction.

14. INDIFFERENCE CURVE (cont.)
An indifference curve represents all those combinations of two goods; X and Y which yield the same level of satisfaction to a consumer.

15. INDIFFERENCE MAP
An indifference map shows a set of indifference curve.
The higher the indifference curve from the origin, higher will be the utility. IC3 has the higher satisfaction.

16. INDIFFERENCE CURVE Marginal Rate of Technical Substitution
Refers to the rate at which one good is substituted for another good.
Characteristics of Indifference Curve
Indifference curve slopes downward from left to right.
Indifference curve are convex to the origin.
Higher indifference curves represent higher level of satisfaction.
Indifference curve never intersect each other.
Indifference curve does not touch the Y axis or X axis.

17. BUDGET LINE
A budget line represents various combinations of two goods, which can be purchased with a given amount of money at the given price of each unit.

18. CHANGES IN BUDGET LINE 1. Change in Consumer’s Income
An increase in consumer’s income will lead to a shift of the budget line to the right, A1B1.
A decrease in consumer’s income will shift the budget line to the left as represented by A2B2.

19. CHANGES IN BUDGET LINE (cont.)
2. Change in Price of Good X
Budget Line AB
A1B1 5 10 15 20 25 30 2 4 6 8 12 14
Good X
Good Y
Good X
Budget Line 10 20 30 2 4 6 8 12 14 16 18 22 24
Good Y AB
A1B1
Price of good X increase from RM1 to RM2 and price of good Y constant.
Price of good X decrease from RM1 to RM0.50 and price of good Y constant.

20. CHANGES IN BUDGET LINE (cont.)
3. Change in Price of Good Y
Budget Line AB
AB1 5 10 15 20 25 30 2 4 6 8 12 14
Good X
Good Y
Budget Line AB
AB1 5 10 15 20 25 30 2 4 6 8 12 14
Good X
Good Y
Price of good Y increase from RM0.50 to RM1 and price of good X constant.
Price of good Y decrease from RM0.50 to RM0.40 and price of good X constant.

21. CONSUMER EQUILIBRIUM
At point b, and e, the consumer will
have a lesser satisfaction at IC3
with the same amount of income
A consumer is in equilibrium when he or she is consuming the best possible
combination of two goods with the given amount of income.
Consumer equilibrium is reached when
indifference curve tangent with budget
Line which represents best combination of two goods with limited income
as point C.

22. INCOME, PRICE AND SUBSTITUTION EFFECT
INCOME EFFECT
The income effect is defined as the effect on the purchases of the consumer caused by changes in income with prices of goods remaining constant.
PRICE EFFECT
Price effect explains what happens to the consumers’ equilibrium position when the price of one good changes while the price of another good and other factors remains constant.
SUBSTITUTION EFFECT
Substitution effect explains what happens to the consumers’ equilibrium position when the price of both good changes—price of one rises and price of another falls while other factors remains constant.

23. CONSUMER SURPLUS Consumer surplus is defined as the excess of what
a consumer is willing to pay and what he/she actually pays.
CONSUMER SURPLUS
Example : Suppose Sally who is fond of chocolates is ready to pay for each successive bar of chocolate as shown in table below. Assume that Sally is willing to pay lower price for the successive bar of chocolates. Assume the market price of one bar of chocolate is RM1.00.
CONSUMER SURPLUS = TOTAL VALUE – (MARKET PRICE x NUMBER OF UNITS CONSUMED)
Price (RM)
Quantity
2.50
1.00 4 DD
CONSUMER SURPLUS
Bars of chocolate 1 2 3 4 5
Price (RM)
2.50
2.00
1.50
1.00
0.80
Consumer surplus = ( ) – (1 x 4)
= RM3.00