Chapter 4
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Chapter 4. Individual and Market Demand. Topics to be Discussed. Individual Demand Income and Substitution Effects Market Demand Consumer Surplus. Individual Demand. Demand curve can be derived from consumption choices made by consumer who is faced with budget constraint Price Changes

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Chapter 4

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Chapter 4

Chapter 4

Individual and Market Demand


Topics to be discussed

Topics to be Discussed

  • Individual Demand

  • Income and Substitution Effects

  • Market Demand

  • Consumer Surplus

Chapter 4


Individual demand

Individual Demand

  • Demand curve can be derived from consumption choices made by consumer who is faced with budget constraint

  • Price Changes

    • The impact of a change in the price can be illustrated using indifference curves.

    • For each price change, we can determine how much of the good the individual would purchase given their budget lines and indifference curves

    • When there is a decrease in price, the budget line will rotate outward (Q↑), while when the price increase the budget line will rotate inward (↓Q).

Chapter 4


Change in price price effect and the demand curve

Change in price (price effect and the demand curve)

Q cloth

1. Assume Y= $20, Pc = $2 and Pf = $2, $1 and 0.50.

2. Initial equilibrium = A, consume 6C and 4F

3. Suppose there is a fall in the price of food from $2 to $1 (Pc unchanged)

4. Lower Pf  rotates the budget line outward  new equilibrium at B (consume 4C & 12F)

5. Suppose Pf reduce to $0.50, budget line rotates outward further  new equilibrium at C (consume 3C & 20F)

6. The equilibrium points A, B and C used to derive demand curve for food.

7. At every point on DD curve – consumer is maximizing utility by satisfying MRS = Pf/Pc

Price-consumption

curve

6

●A

I1

●B

4

●C

3

I2

I3

20

12

4

Q food

P food

●A’

$2

●B’

$1

●C’

.50

DD

12

4

20

Q food

Chapter 4


Individual demand curves important properties

Individual Demand Curves – Important Properties

  • The level of utility changes as we move along the curve (the lower the price of product, the higher the consumer’s purchasing power and the higher its level of utility).

  • At every point on the demand curve, the consumer is maximizing utility by satisfying the condition that the MRS = Pf / Pc .

  • If the price consumption curve is downward-sloping, the two goods are considered substitutes.

  • If the price consumption curve is upward-sloping, the two goods are considered complements.

Chapter 4


Effect of a price change

Price

of Food

E

$2.00

G

$1.00

$.50

H

Food (units

per month)

4

12

20

Demand Curve

Effect of a Price Change

When the price falls:

Pf/Pc & MRS also fall

  • E: Pf/Pc = 2/2 = 1 = MRS

  • G: Pf/Pc = 1/2 = .5 = MRS

  • H:Pf/Pc = .5/2 = .25 = MRS

Chapter 4


Individual demand1

Individual Demand

  • Income Changes

    • Changing income, with prices fixed, causes consumer to change their market baskets.

    • An increase in income shifts the budget line to the right, increasing consumption along the income-consumption curve.

    • Simultaneously, the increase in income shifts the demand curve to the right.

    • The income-consumption curve traces out the utility-maximizing combinations of food and clothing associated with every income level.

Chapter 4


Chapter 4 4522144

Income changes (income effect & change in demand)

1. Assume Pc = $1 and Pf = $2, and Y= $10, $20 and $30

2. Initial equilibrium = A, consume 3C and 4F

3. Suppose there is a  in the income from $10 to $20  there will be a parallel shift outward of budget line  new equilibrium at B (consume 5C & 10F)

4. Suppose Y  to $30  budget line shifts outward again  new equilibrium at C (consume 7C & 16F)

5. Higher income implies consumer will increase their consumption of both goods

6. The effect of income changes are shown with a shift of demand curve to right.

Q cloth

income-consumption

curve

7

●C

5

I3

●B

●A

3

I2

I1

16

Q food

10

4

P food

●B’

●A’

●C’

$2

D3

D1

D2

10

16

4

Q food

Chapter 4


Chapter 4 4522144

Normal versus Inferior

  • Income Changes

    • When the income-consumption curve has a positive slope:

      • The quantity demanded increases with income.

      • The income elasticity of demand is positive.

      • The good is a normal good.

    • When the income-consumption curve has a negative slope:

      • The quantity demanded decreases with income.

      • The income elasticity of demand is negative.

      • The good is an inferior good.

Chapter 4


Chapter 4 4522144

Steak

5

U2

B

3

U1

A

4

10

Effects of Income Changes on inferior goods

An increase in income, with the prices fixed,

causes consumers to alter their choice of

market basket.

Hamburger is a normal good between point A and B.

But becomes an inferior good when the income consumption curve bends backward between B and C.

● C

U3

Hamburger

Chapter 4


Engel curves

Engel Curves

  • Income-consumption curves can be used to construct Engel curves

  • Engel Curves

    • Engel curves relate the quantity of good consumed to income.

    • If the good is a normal good, the Engel curve is upward sloping.

    • If the good is an inferior good, the Engel curve is downward sloping.

Chapter 4


Engel curves1

Income

($ per

month)

30

20

10

Food (units

per month)

4

8

12

16

Engel Curves

Engel curves slope

upward for

normal goods.

Chapter 4


Engel curves2

Income

($ per

month)

30

20

10

Hamburger

4

8

12

16

Engel Curves

●C

Inferior

●B

Normal

●A

Chapter 4


Income and substitution effects

Income and Substitution Effects

  • A change in the price of a good has two effects:

    i. Substitution Effect

    • Relative price of a good changes when price changes

    • Consumers will tend to buy more of the good that has become relatively cheaper, and less of the good that is relatively more expensive.

      ii. Income Effect

    • Consumers experience an increase in real purchasing power when the price of one good falls.

Chapter 4


Income and substitution effects1

Income and Substitution Effects

  • Substitution Effect

    • The substitution effect is the change in an item’s consumption associated with a change in the price of the item, with the level of utility held constant.

    • When the price of an item declines, the substitution effect always leads to an increase in the quantity demanded of the good.

Chapter 4


Income and substitution effects2

Income and Substitution Effects

  • Income Effect

    • The income effect is the change in an item’s consumption brought about by the increase in purchasing power, with the price of the item held constant.

    • When a person’s income increases, the quantity demanded for the product may increase or decrease.

Chapter 4


Income and substitution effects normal good

R

The substitution effect,F1E,

(from point A to D), changes the

relative prices but keeps real income

(satisfaction) constant.

C1

A

D

Substitution

Effect

U1

F1

E

Total Effect

Income and Substitution Effects: Normal Good

When the price of food falls, consumption increases by F1F2 as the consumer moves from A to B.

Clothing

(units per

month)

U2

The income effect, EF2,

( from D to B) keeps relative

prices constant but

increases purchasing power.

●B

C2

Food (units

per month)

F2

T

O

Chapter 4


Chapter 4 4522144

Since food is an

inferior good, the

income effect is

negative. However,

the substitution effect

is larger than the

income effect.

B

U2

Total Effect

Income Effect

Income and Substitution Effects: Inferior Good

Clothing

(units per

month)

R

A

D

Substitution

Effect

U1

Food (units

per month)

F2

O

F1

E

S

T

Chapter 4


Income and substitution effects3

Income and Substitution Effects

  • A Special Case--The Giffen Good

    • The income effect may theoretically be large enough to cause the demand curve for a good to slope upward.

    • This rarely occurs and is of little practical interest.

    • Giffen good – good whose demand curve slopes upward because the (negative) income effect is larger than the substitution effect

Chapter 4


Income and substitution effects giffen good

Income and Substitution Effects: Giffen Good

Clothing

(units per

month)

Substitution effect = EF2

Income effect = F1 F2

Total effect = F1 E

IE > SE

R

B

U2

A

D

Substitution

Effect

U1

Food (units

per month)

O

F1

E

F2

S

T

Income

Effect

Chapter 4


Market demand

Market Demand

Market Demand Curves

  • A curve that relates the quantity of a good that all consumers in a market buy to the price of that good.

  • The sum of all the individual demand curves in the market

  • Market demand curve will shift to the right as more consumer enter market

  • Factors that influence the demands of many consumers will also affect market demand.

Chapter 4


Determining the market demand curve

Determining the Market Demand Curve

Chapter 4


Summing to obtain a market demand curve

Price

5

4

3

Market Demand

2

1

DA

DB

DC

0

Summing to Obtain aMarket Demand Curve

The market demand

curve is obtained by

summing the consumer’s

demand curves

Quantity

5

10

15

20

25

30

Chapter 4


Consumer surplus

Consumer Surplus

  • Consumers buy goods because it makes them better off

  • Consumer Surplus measures how much better off they are

  • It is a difference between what a consumer is willing to pay for a good and the amount they actually paid

Chapter 4


Consumer surplus example

Market Price

Consumer Surplus: Example

  • Demand curve shows the willingness to pay for each concert ticket

  • 1st ticket worth $20 but price is $14 so consumer generates $6 worth of surplus

  • 2nd ticket worth $19 but market P= $14, consumer surplus =$5

  • 3rd ticket = $18, Market p=$14, so CS = $4………..=21

  • Will not buy more than 7 ticket because surplus is negative

  • Thus, total surplus is addition of surplus for each ticket purchased

20

19

18

17

16

Consumer Surplus

6 + 5 + 4 + 3 + 2 + 1 = 21

15

14

13

2

0

3

4

5

6

1

Chapter 4

Concert Tickets


Consumer surplus1

Consumer Surplus

  • The stepladder demand curve can be converted into a straight-line demand curve by making the units of the good smaller.

  • Consumer surplus is area under the demand curve and above the price

Chapter 4


Consumer surplus2

Market Price

Demand Curve

Actual

Expenditure

= $14 X 6500 = $91,000

Consumer Surplus

Price

($ per

ticket)

Consumer Surplus

for the Market Demand

20

19

CS = ½ ($20 - $14)*(6500) = $19,500

18

17

16

Consumer

Surplus

15

14

13

0

1

2

3

4

5

6

Concert Tickets (thousand)

Chapter 4


Summary

Summary

  • Individual Demand

  • Effects of price and income changes

    • price consumption curve and income consumption curve

    • Engel curves : normal and inferior

    • Income and Substitution Effects

      • Normal, Inferior and Giffen goods

  • Market Demand

  • Consumer Surplus

Chapter 4


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