1. Introduction to Economics Eco 101
Lecture# 4
Consumer behavior
Cardinal Approach

2. The Theory of Consumer Behavior
The principle assumption upon which the theory of consumer behavior is built is: a consumer attempts to allocate his/her limited money income among available goods and services so as to maximize his/her utility (satisfaction).

3. Theories of Consumer Choice
The Marginal utility Analysis or Cardinal Approach
Utility is measurable in a cardinal sense
The Indifference Curve Analysis or Ordinal Approach
Utility is measurable in an ordinal sense

4. Utility Utility is want satisfying power
The utility of a good and service is the satisfaction or pleasure one gets from consuming it
It is a subjective satisfaction derived from consumption, it means it can vary from person to person. e.g. eyeglasses can have greater utility for a person having poor eyesight ,while no utility for a person having clear vision.

5. Total and Marginal Utility
Total Utility (TU) is the satisfaction that a consumer receives from all units of a product consumed within a given time period
Marginal Utility (MU) - the change in total utility when consumption of a good changes by one unit.
MU = DTU / D Q consumed of a good 9

6. Law of Diminishing MU Example
The law of diminishing marginal utility states that the more of a product the consumer has, the less will be its marginal utility.
If a person started using some product eventually, a point is reached where the marginal utility obtained by consuming additional units of a good starts to decline.
Example
If you are really hungry, you get a lot of satisfaction from first slice of pizza.
If you keep eating pizza, the satisfaction from the 8th slice would be much less than that of the first slice.

7. Relationship between Total Utility and Marginal Utility10 20 30 8 6 4 2 -2 1 3 5 7
Total Utility
Marginal Utility
(1)
Quantity consumed
(2)
Total
Utility,
(3)
Marginal
Utility, TR 1 2 3 4 5 6 7 10 18 24 28 30 ] 10 8 6 4 2 -2
Units Consumed
Marginal Utility MU
Units Consumed 7

8. The Marginal Utility Curves
As people have different tastes and preferences so the marginal utility curves are also different.
First, Marginal utility may fall sharply as the consumption rises. this means the consumer want is fully satisfied for a few units of a product .As the previous example of pizza is showing the instant satisfaction MU Q

9. The Marginal Utility Curves
Second, marginal utility may fall gently as consumption rises. The consumer want is slowly filled up as consumption rises
For example you are buying 6 shirts in a year. But if you are offered another 6 shirts you will not possibly refuse. thus MU will fall slowly MU Q

10. The Marginal Utility Curves
Third, the marginal utility can be always negative. If you dislike chicken or never touch it, the MU will remain in negative zone for any quantity of consumption. MU Q

11. Equilibrium conditions in cardinal approach
In case of a single commodity  (x)
MUx = Px will be the consumer equilibrium
If MUx > Px – Consumer can increase his welfare by purchasing more units of x
If MUx < Px---- Consumer can increase his total satisfaction by cutting down the quantity of x and keeping more of his income unspent. 11

12. Law of equi-marginal utility/ Utility maximizing Rule
The marginal utility analysis explains how a rational consumer will allocate a given amount of income among different good to achieve the maximum level of satisfaction
The law of marginal utility requires that a consumer Allocate Money Income in such way that Last Dollar Spent on Each Product Yields the Same Marginal Utility
In case of more commodities the equilibrium condition of consumer is equality of ratios of the Marginal utilities of the individual commodities to their prices
MUx/Px= MUy/Py=…..=MUn/Pn

13. Consumer Equilibrium In Multiple Good Case
In case of more commodities the equilibrium condition of consumer is equality of ratios of the Marginal utilities of the individual commodities to their prices
MUx/Px= MUy/Py=…..=MUn/Pn

14. Numerical Example MU
Product X
Units of
Product Y MU
Product Y
Units of
Product X 1 2 3 4 5 14 10 6 4 2 16 12 10 8 6 1 2 3 4 5
Utility-Maximizing Combination of Products X and Y Obtainable with an Income of $5 is the 3 units of x and 2 units of y. As the marginal utilities of last item of both products are equal and total utility is also maximum 62 units.
If consumer chooses any other combination the utility will not be maximized according to law of equi marginal utility as if he purchase 4 units of X and 1 Unit of Y .the utility is is 60 which is less than maximum combination and the utility of last units is also not same.

15. Graphical RepresentationMU 16 14
Maximum satisfaction combination 12 10
Disequilibrium condition 8 6 4
MUX
MUY 2 5 4 3 2 1 1 2 3 4 5 X Y
Units of
Products

16. Consumer Equilibrium with Income Constraint Analysis
If a consumer has to purchase various goods in given money income , he will spend his income in such a way that the marginal utility of last unit of each product should be same.
This equilibrium condition is defined as
MUx/Px= MUy/Py=…..=MUn/Pn in law of equi marginal utility
But we can write this equilibrium condition in another way including the income constraint as XPX+YPY=I
X= quantity of X, Y=quantity of Y I= income PX=price of X PY= price of Y

17. Qx MUx Qy MUy 1 20 7 2 16 6 3 12 5 4 8 If we suppose Px = 2, PY=1, I=8
If consumer purchases 2 units of X and 4 units of Y income constraint function will be
XPx+Ypy = I
2(2)+4(1) =8
8 =8
In consumer equilibrium condition
MUx/Px =MUy/Py
16/2 =4/1
8 = 4

18. This analysis shows the selected combination can not satisfy consumer equilibrium condition as it was failed to satisfy both equations
Suppose consumer choose another combination such as 3 units of X and 2 units of y
The income constraint function will be
XPx+YPy = I
3(2)+2(1) =8
8 =8
Consumer equilibrium condition will be
MUx/Px =MUy/Py
12/2 =6/1
6 =6
This analysis shows this is the equilibrium combination having maximum level of satisfaction within the income constraint.

19. Derivation of an Individual Demand curve from Utility Approach
Based on the law of DMU
MU curve a line with –ve slope
Geometrically The MUx= slope of the total utility as Mu= DU/DQ
Demand curve of good x is identical to the positive segment of the MU curve.

20. Graphical Representation
MUX Px P1
MU1 P2
MU2 Qx Q1 Q2 Qx Q1 Q2

21. Critique of the Cardinal Approach
The satisfaction derived from various commodities can not be measured objectively as utility is a state of mind
Consumer purchases are mostly based on fashion, habits or customs instead of utility analysis
No careful calculation exists in real life about the cost and benefit analysis