1. Demand and Supply Chapter 3
LIPSEY & CHRYSTAL
ECONOMICS 12e

2. 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?

3. 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.

4. DEMAND, SUPPLY AND PRICE
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.

5. 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.

6. 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.

7. DEMAND Alice’s Demand Schedule Alice’s Demand Curve a b c e d f a b c
Quantity demanded
[dozen per month]
Reference Letter
Price [£ per dozen] 1 2 3
0.50
1.00
2.00
Quantity of Eggs [dozen per month]
Price of eggs [£ per dozen]
3.00
2.50 6 5 4 7 a b c e d f
1.50 a b c d e f
0.50
1.00
1.50
2.00
2.50
3.00
7.0
5.0
3.5
2.5
1.5
1.0

8. 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’.

9. 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.

10. The Relation Between Individual and Market Demand Curves
3.00
2.00
Price of eggs [£ per dozen]
1.00
3.00 2 4 6 8
[i]. William
Quantity of Eggs
[dozen per month]
2.00
Price of eggs [£ per dozen]
1.00
3.00 2 4 6 8 10 12 14
2.00
Price of eggs [£ per dozen]
Quantity of Eggs
[dozen per month]
1.00
[iii]. Total Demand William & Sarah 2 4 6 8
[ii]. Sarah
Quantity of Eggs
[dozen per month]

11. 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.

12. A Market Demand Schedule for Eggs
Quantity demanded
[000 dozen per month]
Reference Letter
Price [£ per dozen] U V W X Y Z
0.50
1.00
1.50
2.00
2.50
3.00
110.0
90.0
77.5
67.5
62.5
60.0

13. A Market Demand Schedule for Eggs
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.

14. A Market Demand Curve for Eggs
3.50 D Z
3.00 Y
2.50 X
2.00
Price of eggs [£ per dozen] W
1.50 V
1.00 U
0.50 20 40 60 80
100
120
140
Quantity of Eggs (000/month)

15. A Market Demand Curve for Eggs
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.

16. Quantity of Eggs (000/month)
Two Demand Curves for Eggs
3.50 D0
3.00 Z
2.50 Y
2.00 X
Price of eggs [£ per dozen]
1.50 W V
1.00 U
0.50 20 40 60 80
100
120
140
Quantity of Eggs (000/month)

17. A Market Demand Schedule for Eggs when income rises
Quantity demanded
[000 dozen per month] when income rises
Quantity demanded
[000 dozen per month]
Reference Letter
Price [£ per dozen] U V W X Y Z
0.50
1.00
1.50
2.00
2.50
3.00
110.0
90.0
77.5
67.5
62.5
60.0
140.0
116.0
100.0
90.0
81.3
78.0 U’ V’ W’ X’ Y’ Z’

18. Quantity of Eggs (000/month)
Two Demand Curves for Eggs
3.50 D1 D0
3.00 Z Z’
2.50 Y Y’
2.00 X X’
Price of eggs [£ per dozen]
1.50 W W’ V’ V
1.00 U’ U
0.50 20 40 60 80
100
120
140
Quantity of Eggs (000/month)

19. 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’).

20. Shifts in the Demand Curve
Price
Quantity

21. Shifts in the Demand Curve
An increase in demand D0 D1
Price
Quantity

22. Shifts in the Demand Curve
A decrease in demand D0 D2
Price
Quantity

23. Shifts in the Demand Curve
Price
Quantity

24. 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.

25. 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.

26. 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.

27. 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.

28. 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.

29. 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.

30. 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?’

31. 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.

32. 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.

33. 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.

34. 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.

35. 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.

36. 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.’

37. A Market Supply schedule for Eggs
Quantity demanded
[000 dozen per month]
Reference Letter
Price [£ per dozen]
5.0
0.50 u
46.0
1.00 v
77.5
1.50 w
100.0 x
2.00
115.0 y
2.50
122.5 z
3.00

38. 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.

39. A Supply Curve For Eggs 3.50 S Z 3.00 Y 2.50 X 2.00
Price of eggs [£ per dozen] W
1.50 V
1.00 U
0.50 20 40 60 80
100
120
140
Quantity of Eggs[thousand dozen per month]

40. 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.

41. Two Alternative Market Supply Schedule for Eggs
Price of Eggs
[£ per dozen]
Original quantity
supplied [‘000
dozen per month]
New quantity
supplied [‘000
dozen per month]
[1]
[2]
[3]
[4]
[5] u
0.50
5.0
28.0 U’ v
1.00
46.0
76.0 V’ w
1.50
77.5
102.0 W’ x
2.00
100.0
120.0 X’ y
2.50
115.0
132.0 Y’ z
3.00
122.5
140.0 Z’

42. Two Supply Curves for Eggs
3.50 S0 Z
3.00 Y
2.50 X
2.00 W
Price of eggs [£ per dozen]
1.50 V
1.00 U
0.50 20 40 60 80
100
120
140
Quantity of Eggs [thousand dozen per month]

43. Two Supply Curves for Eggs
3.50 S0 S1 Z
3.00 Y
2.50 X
2.00 W
Price of eggs [£ per dozen]
1.50 V
1.00 U
0.50 20 40 60 80
100
120
140
Quantity of Eggs [thousand dozen per month]

44. 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.

45. Shifts in the Supply Curve
Price
Quantity

46. Shifts in the Supply Curve – increase in supply
Price
Quantity

47. Shifts in the Supply Curve – decrease in supply
Price
Quantity

48. Shifts in the Supply Curve
Price
Quantity

49. 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).

50. The determination of price
So far we have considered demand and supply separately.
We now outline how demand and supply interact to determine price.

51. 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.

52. Excess Demand [quantity
Demand and Supply Schedules for Eggs and Equilibrium Price
Price
[£ per dozen]
Quantity
demanded
[‘000 dozen
per month]
Quantity supplied
[‘000 dozen
per month]
Excess Demand [quantity
demanded minus
quantity supplied]
[‘000 dozen per month]
0.50
110.0
5.0
105.0
1.00
90.0
46.0
44.0
1.50
77.5
77.5
0.0
2.00
67.5
100.0
-32.5
2.50
62.5
115.0
-52.5
3.00
60.0
122.5
-62.5

53. 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.

54. Determination of the Equilibrium Price of Eggs
3.50 S D Z Z
3.00 Y Y
2.50 X X
2.00
Price of eggs [£ per dozen]
1.50 W W V V
1.00 U U
0.50 20 40 60 80
100
120
140
Quantity of Eggs [thousand dozen per month]

55. 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.

56. The ‘Laws’ of Demand and Supply
Price
Price E1 E0 p1 E0 p0 E1 p0 p1
Quantity q0 q1
Quantity q0 q1
[i]. The effects of shifts in the demand curve
[ii]. The effects of shifts in the supply curve

57. 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.

58. 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.