Demand and SupplyChapter 3

LIPSEY & CHRYSTAL

ECONOMICS 12e

Introduction

• Some initial opening questions:• Why does the price of computers keep falling while train

fares keep rising?• How do markets work and what factors influence the

outcomes?• Who are the participants in markets and what motivates

them?• What are the main factors that influence how much of a

product consumers wish to buy?• What are the main factors that influence how much

producers wish to sell?

Learning outcomes

• The participants in markets and what motivates them.• The main factors that influence how much of a product

consumers wish to buy.• The main influences on how much producers wish to

sell.• How consumers and producers interact to determine the

market price.• While demand and supply forces are present in all

markets, many different institutional structures also affect market outcomes.

Demand• An individual consumer’s demand curve shows the relation

between the price of a product and the quantity of that product the customer wishes to purchase per period of time.

• It is drawn on the assumption that all other prices, income, and tastes remain constant.

• Its negative slope indicates that the lower the price of the product, the more the consumer wishes to purchase.

• The market demand curve is the horizontal sum of all the individual consumers.

DEMAND, SUPPLY AND PRICE

Demand

• In formulating our demand theory, the agents are all assumed to be adult individuals who earn income, and they spend this income purchasing various goods and services.

• The consumer ‘is assumed to ‘maximize utility’ within the limits set by his or her available resources.

The nature of demand

• The amount of a product that consumers wish to purchase is called the quantity demanded.

• Note there are two important things about this concept.

• First, quantity demanded is a desired quantity.• Secondly, quantity demanded is a flow.

Alice’s Demand Schedule

Reference Letter Price [£ per dozen] Quantity demanded [dozen per month]

abcdef

Alice’s Demand Curve

1 2 3

0.50

1.00

2.00

Quantity of Eggs [dozen per month]

Pric

e o

f e

gg

s [£

pe

r d

oze

n]

3.00

2.50

654 7

a

b

c

e

d

f

1.50

DEMAND

0.501.001.502.002.503.00

7.05.03.52.51.51.0

Alice’s demand schedule for eggs

· The table shows the quantity of eggs that Alice will demand at each selected price, other things being equal.

· For example, at a price of £1.00, Alice demands 5 dozen eggs per month.

· The data is plotted in the figure ‘Alice’s demand curve’.

Alice’s demand curve

· Each point on the figure relates to a row on Table Demand Schedule.

· For example, when price is £3.00, 1 dozen are brought per month (point f ).

· When the price is £0.50, 7 dozen are brought (point a).

· The resulting curve relates the price of a commodity to the amount that Alice wishes to purchase.

2 4 6 8 10 12

2 4 6

1.00

2.00

3.00

1.00

2.00

3.00

8

14

Quantity of Eggs[dozen per month]

Quantity of Eggs[dozen per month]

Pric

e o

f e

gg

s [£

pe

r d

oze

n]

Pric

e o

f e

gg

s [£

pe

r d

oze

n]

The Relation Between Individual and Market Demand Curves

[i]. William

[ii]. Sarah

[iii]. Total Demand William & Sarah

2 4 6

1.00

2.00

3.00

Quantity of Eggs[dozen per month]

Pric

e o

f e

gg

s [£

pe

r d

oze

n]

8

The relation between individual and market demand curves

· The figure illustrates aggregation over two individuals, William and Sarah.

· For example, at a price of £2.00 per dozen William purchases 2.4 dozen and Sarah purchases 3.6 dozen.

· Together they purchase 6 dozen. · In general the market demand curve is the

horizontal sum of the demand curves of all consumers in the market.

A Market Demand Schedule for Eggs

Reference Letter Price [£ per dozen]Quantity demanded

[000 dozen per month]

0.50

1.00

1.50

2.00

2.50

3.00

110.0

90.0

77.5

67.5

62.5

60.0

U

V

W

X

Y

Z

· The table shows the quantity of eggs that would be demanded by all consumers at selected prices, ceteris paribus.

· For example, row W indicates that if the price of eggs were £1.50 per dozen, consumers would want to purchase 77,500 dozen per month.

· The data in this table are plotted in the following figure.

A Market Demand Schedule for Eggs

Quantity of Eggs (000/month)

20 40 60 80 100 120

1.00

2.00

3.00

140

Pric

e o f

egg

s [ £

per

do

zen]

A Market Demand Curve for Eggs

2.50

1.50

3.50

0.50

Z

D

Y

X

W

V

U

• The negative slope of the curve indicates that quantity demanded increases as price falls.

• The six points correspond to the six price–quantity combinations shown in the table.

• The curve drawn through all of the points and labelled D is the demand curve.

A Market Demand Curve for Eggs

20 40 60 80 100 120

1.00

2.00

3.00

140Quantity of Eggs (000/month)

Pric

e o f

egg

s [ £

per

do

zen]

Two Demand Curves for Eggs

2.50

1.50

3.50

0.50

Z

D0

Y

X

W

V

U

A Market Demand Schedule for Eggs when income rises

Reference Letter Price [£ per dozen]Quantity demanded

[000 dozen per month]

0.50

1.00

1.50

2.00

2.50

3.00

140.0

116.0

100.0

90.0

81.3

78.0

Quantity demanded [000 dozen per

month] when income rises

110.0

90.0

77.5

67.5

62.5

60.0

U’

V’

W’

X’

Y’

Z’

U

V

W

X

Y

Z

20 40 60 80 100 120

1.00

2.00

3.00

140

Pric

e o f

egg

s [ £

per

do

zen]

2.50

1.50

3.50

0.50

Z

D0

Y

X

W

V

U

D1

Z’

Y’

X’

W’

V’

U’

Two Demand Curves for Eggs

Quantity of Eggs (000/month)

Two demand curves for eggs

· When the curve shifts from D0 to D1, more is demanded at each price and a higher price is paid for each quantity.

· At price £1.50, quantity demanded rises from 77.5 thousand dozen (point W) to 100 (point W’).

· The quantity of 90 thousand dozen, which was formerly bought at a price of £1.00 (point V), will be brought at a price of £2.00 after the shift (point X’).

D0

Pric

e

Quantity

0

Shifts in the Demand Curve

D0

Quantity0

Pric

e

Shifts in the Demand Curve An increase in demand

D1

D0

Quantity0

Pric

e

Shifts in the Demand Curve A decrease in demand

D2

D2 D0 D1

Quantity0

Pric

eShifts in the Demand Curve

Note

• A rise in the price of a product’s substitute shifts the demand curve for the product to the right. More will be purchased at each price.

• A fall in the price of one product that is complementary to a second product will shift the second product’s demand curve to the right. More will be purchased at each price.

Movements along demand curves versus shifts

• Demand refers to one whole demand curve.

• Change in demand refers to a shift in the whole curve, that is, a change in the amount that will be bought at every price.

Note

An increase in demand means that the whole demand curve has shifted to the right; a decrease in demand means that the whole

demand curve has shifted to the left.

• Any one point on a demand curve represents a specific amount being bought at a specified price. It represents, therefore, a particular quantity demanded.

Note

A movement down a demand curve is called an increase (or a rise) in the quantity

demanded; a movement up the demand curve is called a decrease (or a fall) in the

quantity demanded.

• A movement along a demand curve is referred to as a change in the quantity demanded.

Shifts in the demand curve

· When the demand curve shifts from D0 to D1, more is demanded at each price.

· Such an increase in demand can be caused by:· A rise in the price of a substitute· A fall in the price of a complement· A rise in income· A redistribution of income towards those who

favour the commodity · A change in tastes that favours the commodity.

Shifts in the demand curve

· When the demand curve shifts from D0 to D2, less is demanded at each price.

· Such a decrease in demand can be caused by:· a fall in the price of a substitute · a rise in the price of a complement, a fall in

income· a redistribution of income away from groups that

favour the commodity · a change in tastes that dis-favours the

commodity.

Demand and price

• We are interested in developing a theory of how products get priced.

• To do this, we hold all other influences constant and ask the following question:

‘How will the quantity of a product demanded vary as its own price varies?’

Note

A basic economic hypothesis is that the lower the price of a product, the larger the

quantity that will be demanded, other things being equal.

Supply

• We now look at the supply side of markets. The suppliers are firms, which are in business to make the goods and services that consumers want to buy.

Firms’ motives

• Economic theory gives firms several attributes.

• Firstly, each firm is assumed to make consistent decisions, as though it was run by a single individual decision-maker.

• Secondly, firms hire workers and invest capital and entrepreneurial talent in order to produce goods and services that consumers wish to buy.

• Thirdly, firms are assumed to make their decisions with a single goal in mind: to make as much profit as possible.

The nature of supply

• The amount of a product that firms are able and willing to offer for sale is called the quantity supplied.

• Supply is a desired flow: how much firms are willing to sell per period of time, not how much they actually sell.

The determinants of quantity supply

• Three major determinants of the quantity supplied in a particular market are:– the price of the product;– the prices of inputs to production;– the state of technology.

Supply and price

• For a simple theory of price, we need to know how quantity supplied varies with a product’s own price, all other things being held constant.

‘The quantity of any product that firms will produce and offer for sale is positively

related to the product’s own price, rising when the price rises and falling when the

price falls.’

A Market Supply schedule for Eggs

Reference Letter Price [£ per dozen] Quantity demanded [000 dozen per month]

w

y

u

v

z

x

0.50

1.00

2.00

2.50

1.50

5.0

77.5

100.0

3.00

46.0

122.5

115.0

A market supply schedule for eggs

· The table shows the quantities that producers wish to sell at various prices, ceteris paribus.

· For example, row y indicates that if the price were £2.50, producers would wish to sell 115,000 dozen eggs per month.

· The data in this table are plotted in the following figure.

20 40 60 80 100 120

1.00

2.00

3.00

140

Quantity of Eggs[thousand dozen per month]

Pric

e o f

egg

s [ £

per

do

zen]

A Supply Curve For Eggs

2.50

1.50

3.50

0.50

ZS

Y

X

W

V

U

A supply curve for eggs

· The six points correspond to the price-quantity combinations shown in Table ‘A Market Supply Schedule for Eggs’.

· The curve drawn through these points, labeled S, is the supply curve showing the quantity of eggs that will be supplied at each price of eggs.

· The supply curve’s positive slope indicates that quantity supplied increases as price increases.

Two Alternative Market Supply Schedule for Eggs

[1]

Price of Eggs[£ per dozen]

New quantity supplied [‘000

dozen per month]

w

y

u

v

z

x

0.50

1.00

2.00

2.50

1.50

5.0

77.5

100.0

3.00

46.0

122.5

Original quantitysupplied [‘000

dozen per month]

115.0

28.0

76.0

102.0

120.0

132.0

140.0

U’

V’

W’

X’

Y’

Z’

[2] [3] [4] [5]

20 40 60 80 100 120

1.00

2.00

3.00

140

Quantity of Eggs [thousand dozen per month]

Two Supply Curves for Eggs

2.50

1.50

3.50

0.50

Z

S0

Y

X

W

V

UPric

e o f

egg

s [ £

per

do

zen]

20 40 60 80 100 120

1.00

2.00

3.00

140

Quantity of Eggs [thousand dozen per month]

Pric

e o f

egg

s [ £

per

do

zen]

2.50

1.50

3.50

0.50

Z

S0

Y

X

W

V

U

S1

Two Supply Curves for Eggs

Two supply curves for eggs

· The rightward shift in the supply curve from S0

to S1 indicates an increase in the quantity supplied at each price.

· For example, at the price of £1.00 the quantity supplied rises from 46 to 76 thousand dozen per month.

Quantity

Pric

e

Shifts in the Supply Curve

S0

Quantity

Pric

e

S0 S1

Shifts in the Supply Curve – increase in supply

Quantity

Pric

e

S2 S0

Shifts in the Supply Curve – decrease in supply

Quantity

Pric

e

S2 S0 S1

Shifts in the Supply Curve

Shifts in the supply curve

· A shift in the supply curve from S0 to S1 indicates more is supplied at each price.

· Such an increase in supply can be caused by:· Improvements in the technology of producing the commodity· A fall in the price of inputs that are important in producing the

commodity· A shift in the supply curve from S0 to S2 indicates less is supplied

at each price.· Such a decrease in supply can be caused by:

· A rise in the price of inputs that are important in producing the commodity.

· Changes in technology that increase the costs of producing the commodity (rare).

The determination of price

• So far we have considered demand and supply separately.

• We now outline how demand and supply interact to determine price.

The concept of a market

• A market may be defined as an area over which buyers and sellers negotiate the exchange of some product or related group of products.

• It must be possible, therefore, for buyers and sellers to communicate with each other and to make meaningful transactions over the whole market.

Demand and Supply Schedules for Eggs and Equilibrium Price

Price [£ per dozen]

Quantity supplied [‘000 dozen per month]

0.50

1.00

2.00

2.50

1.50

110.0

77.5

67.5

3.00

90.0

60.0

Quantity demanded [‘000 dozenper month]

62.5

5.0

46.0

77.5

100.0

115.0

122.5

105.0

44.0

0.0

-32.5

-52.5

-62.5

Excess Demand [quantity demanded minus quantity supplied]

[‘000 dozen per month]

Demand and supply schedules for eggs and equilibrium price

· Equilibrium occurs where the quantity demanded and the quantity supplied are equal.

· In the table the equilibrium price is £1.50.· The equilibrium quantity bought and sold is 77.5 thousand

dozen per month.· For prices below the equilibrium, such as £0.50, quantity

demanded (110) exceeds quantity supplied (5).· For prices above the equilibrium, such as £3.00, quantity

demanded (60) is less than quantity supplied (122.5).· The data in this table are plotted in the following figure.

20 40 60 80 100 120

1.00

2.00

3.00

140

Quantity of Eggs [thousand dozen per month]

Pric

e o f

egg

s [ £

per

do

zen] 2.50

1.50

3.50

0.50

Z

S

Y

X

W

V

U

D

U

V

W

X

Y

Z

Determination of the Equilibrium Price of Eggs

Determination of the equilibrium price of eggs

· Equilibrium price is where the demand and supply curves intersect, point E in the figure.

· At all prices above equilibrium there is excess supply and downward pressure on price.

· At all prices below equilibrium there is excess demand and upward pressure on price.

The ‘Laws’ of Demand and Supply

DS

[ii]. The effects of shifts in the supply curveP

rice

QuantityQuantity

Pric

e

[i]. The effects of shifts in the demand curve

S0

q0

E0

p0

p0

E0

q0

p1

p1

q1q1

E1

E1

D1

D0S1

The laws of demand and supply (i) shifts in demand

· The original curves are D0 and S, which intersect to produce equilibrium at E0.

· Price is p0, and quantity q0.

· An increase in demand shifts the demand curve to D1.

· Price rises to p1 and quantity rises to q1 taking the new equilibrium to E1.

· A decrease in demand now shifts the demand curve to D0.

· Price falls to p0 and quantity falls to q0 taking the new equilibrium to E0.

· Thus, an increase in demand raises both price and quantity while a decrease in demand lowers both price and quantity.

The laws of demand and supply (ii) shifts in supply

· The original demand and supply curves are D and S0, which intersect to produce an equilibrium at E0, price p0 and quantity q0.

· An increase in supply shifts the supply curve to S1. Price falls to p1 and quantity rises to q1, taking the new equilibrium to E1.

· A decrease in supply shifts the supply curve back to S0. Price rises to p0 and quantity falls to q0 taking the new equilibrium to E0.

· Thus an increase in supply raises quantity but lowers prices while a decrease in supply lowers quantity but raises price.