ECO 120 - Global
Macroeconomics
TAGGERT J. BROOKS
Module 05
SUPPLY AND DEMAND INTRODUCTION
Supply and Demand:
A Model of a Competitive Market
A
competitive market:

Many buyers and sellers

Same good or service
 The
supply and demand model is a model of how a
competitive market works.
Supply and Demand:
A Model of a Competitive Market
 Five
key elements:

Demand curve

Supply curve

Demand and supply curve shifts

Market equilibrium

Changes in the market equilibrium
The Demand Schedule and
the Demand Curve

A demand schedule
shows how much of a
good or service
consumers will want to
buy at different prices.
Demand Schedule for Coffee Beans
Price of coffee
beans (per
pound)
Quantity of coffee
beans demanded
(billions of pounds)
$2.00
7.1
1.75
7.5
1.50
8.1
1.25
8.9
1.00
10.0
0.75
11.5
0.50
14.2
The Demand Schedule and
the Demand Curve
Price of coffee
bean (per gallon)
A demand curve is the graphical
representation of the demand schedule; it
shows how much of a good or service
consumers want to buy at any given price.
$2.00
1.75
1.50
1.25
1.00
0.75
0.50
0
As price rises,
the quantity
demanded falls
7
9
Demand
curve, D
11
13
15
17
Quantity of coffee beans
(billions of pounds)
Shifts of the Demand Curve

An increase in the
population and other
factors generate an
increase in demand
– a rise in the quantity
demanded at any given
price.
Demand Schedules for Coffee Beans
Price of coffee
beans (per
pound)
$2.00
1.75
1.50
1.25
1.00
0.75
0.50
Quantity of coffee
beans demanded
(billions of pounds)
in 2002
7.1
7.5
8.1
8.9
10.0
11.5
14.2
in 2006
8.5
9.0
9.7
10.7
12.0
13.8
17.0
Shifts of the Demand Curve

This is represented by the
two demand schedules:


One showing demand in 2002,
before the rise in population.
The other showing demand in
2006, after the rise in population.
Demand Schedules for Coffee Beans
Price of coffee
beans (per
pound)
$2.00
1.75
1.50
1.25
1.00
0.75
0.50
Quantity of coffee
beans demanded
(billions of pounds)
in 2002
7.1
7.5
8.1
8.9
10.0
11.5
14.2
in 2006
8.5
9.0
9.7
10.7
12.0
13.8
17.0
Shifts of the Demand Curve
Increase in
population 
more coffee
drinkers
Price of coffee
beans (per gallon)
$2.00
Demand curve
in 2006
1.75
1.50
1.25
1.00
0.75
0.50
0
Demand curve in
2002
7
9
D1
11
13
D2
15
17
Quantity of coffee beans
(billions of pounds)
A shift of the demand curve is a change in the quantity demanded at any given
price, represented by the change of the original demand curve to a new
position, denoted by a new demand curve.
Movement Along
the Demand Curve
Price of coffee beans
(per gallon)
A movement along the demand curve is a
change in the quantity demanded of a
good that is the result of a change in that
good’s price.
A shift of the demand
curve…
$2.00
1.75
A
1.50
… is not the same thing as a
movement along the demand
curve
C
1.25
B
1.00
0.75
0.50
0
D1
7
8.1
9.7
10
13
15
D2
17
Quantity of coffee beans
(billions of pounds)
Shifts of the Demand Curve
A “decrease in demand”, means a
leftward shift of the demand curve: at
any given price, consumers demand a
smaller quantity than before. (D1D3)
Price
Increase in
demand
An “increase in demand” means a
rightward shift of the demand curve: at
any given price, consumers demand a
larger quantity than before. (D1D2)
Decrease in
demand
D3
D1
D2
Quantity
Understanding Shifts of
the Demand Curve
 Changes
in the Prices of Related Goods

Substitutes: Two goods are substitutes if a fall in the price of one of the
goods makes consumers less willing to buy the other good.

Complements: Two goods are complements if a fall in the price of one
good makes people more willing to buy the other good.
Understanding Shifts of
the Demand Curve
 Changes
in Income

Normal Goods: When a rise in income increases the demand for a
good - the normal case - we say that the good is a normal good.

Inferior Goods: When a rise in income decreases the demand for a
good, it is an inferior good.
Understanding Shifts of
the Demand Curve
 Changes
in Tastes
 Changes
in Expectations
Individual Demand Curve and
the Market Demand Curve
(a) Darla’s Individual
Demand Curve
Price of coffee
beans (per
pound)
Price of coffee
beans (per
pound)
$2
Price of coffee
beans (per
pound)
$2
1
$2
1
D
0
(c) Market Demand Curve
(b) Dino’s Individual
Demand Curve
D
Darla
20
30
Quantity of coffee beans
(pounds)
1
0
D Market
Dino
10
20
Quantity of coffee beans
(pounds)
0
30
40
50
Quantity of coffee beans
(pounds)
The market demand curve is the horizontal sum of the individual demand
curves of all consumers in that market.