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Theory of Supply and Demand
2
Overview Market (who, what, how) Supply and demand is an economic model
– Designed to explain how prices are determined in certain types of markets
1. The law of demand2. The law of supply3. The determination of market equilibrium4. Factors shifting demand or supply curves
3
Markets
In economics, a market is not a place but rather a group of buyers and sellers with the potential to trade with each other – Market is defined not by its location but by its
participants– First step in an economic analysis is to define and
characterize the market or collection of markets to analyze
Economists think of the economy as a collection of individual markets
4
How Broadly Should We Define The Market
Defining the market often requires economists to group things together– Aggregation is the combining of a group of distinct
things into a single whole
Markets can be defined broadly or narrowly, depending on our purpose– How broadly or narrowly markets are defined is one of
the most important differences between Macroeconomics and Microeconomics
5
Defining Macroeconomic Markets
Goods and services are aggregated to the highest levels– Macro models lump all consumer goods into the
single category “consumption goods”– Macro models will also analyze all capital goods
as one market– Macroeconomists take an overall view of the
economy without getting bogged down in details
6
Defining Microeconomic Markets
Markets are defined narrowly– Focus on models that define much more
specific commodities
7
Buyers and Sellers
Buyers and sellers in a market can be– Households– Business firms– Government agencies
• All three can be both buyers and sellers in the same market, but are not always
For purposes of simplification we will usually follow these guidelines– In markets for consumer goods, we’ll view business
firms as the only sellers, and households as only buyers– In most of our discussions, we’ll be leaving out the
“middleman”
8
Competition in Markets
In imperfectly competitive markets, individual buyers or sellers can influence the price of the product
In perfectly competitive markets (or just competitive markets), each buyer and seller takes the market price as a given
What makes some markets imperfectly competitive and others perfectly competitive?– Perfectly competitive markets have many small buyers and sellers
• Each is a small part of the market, and the product is standardized
– Imperfectly competitive markets have just a few large buyers and sellers
• Or else the product of each seller is unique in some way
9
Using Supply and Demand
Supply and demand model is designed to explain how prices are determined in perfectly competitive markets– Perfect competition is rare but many markets come
reasonably close– Perfect competition is a matter of degree rather than an
all or nothing characteristic
Supply and demand is one of the most versatile and widely used models in the economist’s tool kit
10
Demand
A household’s quantity demanded of a good– Specific amount household would choose to buy over some
time period, given• A particular price that must be paid for the good• All other constraints on the household
Market quantity demanded (or quantity demanded) is the specific amount of a good that all buyers in the market would choose to buy over some time period, given– A particular price they must pay for the good
– All other constraints on households
11
Quantity Demanded
Implies a choice– How much households would like to buy when they take into account
the opportunity cost of their decisions?
Is hypothetical– Makes no assumptions about availability of the good– How much would households want to buy, at a specific price, given
real-world limits on their spending power?
Stresses price– Price of the good is one variable among many that influences quantity
demanded– We’ll assume that all other influences on demand are held constant, so
we can explore the relationship between price and quantity demanded
12
The Law of Demand
The price of a good rises and everything else remains the same, the quantity of the good demanded will fall – The words, “everything else remains the same”
are important• In the real world many variables change
simultaneously• However, in order to understand the economy we
must first understand each variable separately• Thus we assume that, “everything else remains the
same,” in order to understand how demand reacts to price
13
The Demand Schedule
Demand schedule– A list showing the quantity of a good that
consumers would choose to purchase at different prices, with all other variables held constant
Demand V.S. Quantities demanded - demand is the entire relationship between price and quantity
- quantities demanded are specific amount of goods buyers want to buy
14
The Demand Curve
The market demand curve (or just demand curve) shows the relationship between the price of a good and the quantity demanded , holding constant all other variables that influence demand– Each point on the curve shows the total buyers
would choose to buy at a specific price
Law of demand tells us that demand curves virtually always slope downward
15
Figure 1: The Demand Curve
Number of Bottles per Month
Price per Bottle
A
B
Rs4.00
2.00
D
40,000 60,000
At Rs2.00 per bottle, 60,000 bottles are demanded (point B).
When the price is Rs4.00 per bottle, 40,000 bottles are demanded (point A).
16
“Shifts” vs. “Movements Along” The Demand Curve
Move along the demand curve– From a change in the price of the good we analyze
In maple syrup example, Figure 1– A fall in price would cause a movement to the right along the
demand curve (point A to B)
See figure 3(a)
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Figure 3(a): Movements Along and Shifts of The Demand Curve
Quantity
Price
P2
Q2 Q1 Q3
P1
P3
Price increase moves us leftward along demand curve
Price increase moves us rightward along demand curve
18
“Shifts” vs. “Movements Along” The Demand Curve
Shift of demand curve– a change in other things than price of the good causes a
shift in the demand curve itself, for example, income In Figure 2
– Demand curve has shifted to the right of the old curve (from Figure 1) as income has risen
– A change in any variable that affects demand—except for the good’s price—causes the demand curve to shift
19
Figure 2: A Shift of The Demand Curve
B CRs2.00
60,000 80,000
D1D2
An increase in income shifts the demand curve for maple syrup from D1 to D2.
Number of Bottles per Month
Price per Bottle
At each price, more bottles are demanded after the shift
20
“Change in Quantity Demanded” vs. “Change in Demand”
Language is important when discussing demand– “Quantity demanded” means
• A particular amount that buyers would choose to buy at a specific price
• It is a number represented by a single point on a demand curve• When a change in the price of a good moves us along a
demand curve, it is a change in quantity demand
– The term demand means• The entire relationship between price and quantity demanded
—and represented by the entire demand curve• When something other than price changes, causing the entire
demand curve to shift, it is a change in demand
21
Income: Factors That Shift The Demand Curve
An increase in income has effect of shifting demand for normal goods to the right– However, a rise in income shifts demand for
inferior goods to the leftA rise in income will increase the demand
for a normal good, and decrease the demand for an inferior good
Normal good and inferior good are defined by the relation between demand and income
22
Wealth: Factors That Shift The Demand Curve
Your wealth—at any point in time—is the total value of everything you own minus the total dollar amount you owe
- ExampleAn increase in wealth will
– Increase demand (shift the curve rightward) for a normal good
– Decrease demand (shift the curve leftward) for an inferior good
23
Prices of Related Goods: Factors that Shift the Demand Curve
Substitute—good that can be used in place of some other good and that fulfills more or less the same purpose– Example– A rise in the price of a substitute increases the demand for a
good, shifting the demand curve to the right Complement—used together with the good we are
interested in– Example– A rise in the price of a complement decreases the demand
for a good, shifting the demand curve to the left
24
Other Factors That Shift the Demand Curve
Population– As the population increases in an area
• Number of buyers will ordinarily increase• Demand for a good will increase
Expected Price– An expectation that price will rise (fall) in the future shifts the
current demand curve rightward (leftward) Tastes
– Combination of all the personal factors that go into determining how a buyer feels about a good
– When tastes change toward a good, demand increases, and the demand curve shifts to the right
– When tastes change away from a good, demand decreases, and the demand curve shifts to the left
25
Small Summary-- Factors Affecting Demand
Income (depends on good’s nature: normal or inferior)
Wealth (depends on good’s nature)Prices of substitutes (positively related) Prices of complements (negatively related)Population (positively related)Expected price (positively related)Tastes (positively related)
26
Figure 3(b): Movements Along and Shifts of The Demand Curve
Quantity
Price
D2
D1
Entire demand curve shifts rightward when:• income or wealth ↑• price of substitute ↑• price of complement ↓• population ↑• expected price ↑• tastes shift toward good
27
Figure 3(c): Movements Along and Shifts of The Demand Curve
Quantity
Price
D1
D2
Entire demand curve shifts leftward when:• income or wealth ↓• price of substitute ↓• price of complement ↑• population ↓• expected price ↓• tastes shift toward good
28
Supply
A firm’s quantity supplied of a good is the specific amount its managers would choose to sell over some time period, given– A particular price for the good– All other constraints on the firm
Market quantity supplied (or quantity supplied) is the specific amount of a good that all sellers in the market would choose to sell over some time period, given– A particular price for the good– All other constraints on firms
29
Quantity Supplied
Implies a choice– Quantity that gives firms the highest possible profits when they take
account of the constraints presented to them by the real world Is hypothetical
– Does not make assumptions about firms’ ability to sell the good– How much would firms’ managers want to sell, given the price of
the good and all other constraints they must consider? Stresses price
– The price of the good is just one variable among many that influences quantity supplied
– We’ll assume that all other influences on supply are held constant, so we can explore the relationship between price and quantity supplied
30
The Law of Supply
States that when the price of a good rises and everything else remains the same, the quantity of the good supplied will rise– The words, “everything else remains the same” are
important• In the real world many variables change simultaneously• However, in order to understand the economy we must
first understand each variable separately• We assume “everything else remains the same” in order
to understand how supply reacts to price
31
The Supply Schedule and The Supply CurveSupply schedule—shows quantities of a good
or service firms would choose to produce and sell at different prices, with all other variables held constant
Supply curve—graphical depiction of a supply schedule– Shows quantity of a good or service supplied at
various prices, with all other variables held constant
32
Figure 4: The Supply Curve
F
G
2.00
S
40,000 60,000
Rs4.00
At Rs4.00 per bottle, quantity supplied is 60,000 bottles (point G).
When the price is Rs2.00 per bottle, 40,000 bottles are supplied (point F).
Number of Bottles per Month
Price per Bottle
33
Shifts vs. Movements Along the Supply Curve A change in the price of a good causes a movement
along the supply curve– In Figure 4
• A rise (fall) in price would cause a rightward (leftward) movement along the supply curve
A drop in transportation costs will cause a shift in the supply curve itself– In Figure 5
• Supply curve has shifted to the right of the old curve (from Figure 4) as transportation costs have dropped
• A change in any variable that affects supply—except for the good’s price—causes the supply curve to shift
34
Figure 5: A Shift of The Supply Curve
S2
GJ
S1
60,000
Rs4.00
80,000
A decrease in transportation costs shifts the supply curve for maple syrup from S1 to S2.
Number of Bottles per Month
Price per Bottle
At each price, more bottles are supplied after the shift
35
Factors That Shift the Supply Curve
Input prices– A fall (rise) in the price of an input causes an increase
(decrease) in supply, shifting the supply curve to the right (left)
Price of Related Goods– When the price of an alternate good rises (falls), the
supply curve for the good in question shifts leftward (rightward)
Technology– Cost-saving technological advances increase the supply
of a good, shifting the supply curve to the right
36
Factors That Shift the Supply Curve
Number of Firms – An increase (decrease) in the number of sellers
—with no other changes—shifts the supply curve to the right (left)
Expected Price– An expectation of a future price increase
(decrease) shifts the current supply curve to the left (right)
37
Factors That Shift the Supply Curve
Changes in weather – Favorable weather
• Increases crop yields• Causes a rightward shift of the supply curve for that crop
– Unfavorable weather • Destroys crops• Shrinks yields• Shifts the supply curve leftward
Other unfavorable natural events may effect all firms in an area– Causing a leftward shift in the supply curve
38
Figure 6(a): Changes in Supply and in Quantity Supplied
P2
Q3 Q1 Q2
P1
P3
Quantity
Price Price increase moves us rightward along supply curve
S
Price increase moves us leftward along supply curve
39
Figure 6(b): Changes in Supply and in Quantity Supplied
Quantity
Price
S2
S1Entire supply curve shifts rightward when:• price of input ↓• price of alternate good ↓• number of firms ↑• expected price ↑• technological advance• favorable weather
40
Figure 6(c): Changes in Supply and in Quantity Supplied
Quantity
Price
S1
S2Entire supply curve shifts rightward when:• price of input ↑• price of alternate good ↑• number of firms ↓• expected price ↑• unfavorable weather
41
Summary: Factors That Shift The Supply Curve
The short list of shift-variables for supply that we have discussed is far from exhaustive
In some cases, even the threat of such events can cause serious effects on production
Basic principle is always the same– Anything that makes sellers want to sell more or less of
a good at any given price will shift supply curve
42
Equilibrium: Putting Supply and Demand Together
When a market is in equilibrium– Both price of good and quantity bought and sold have
settled into a state of rest– The equilibrium price and equilibrium quantity are
values for price and quantity in the market but, once achieved, will remain constant
• Unless and until supply curve or demand curve shifts The equilibrium price and equilibrium quantity
can be found on the vertical and horizontal axes, respectively– At point where supply and demand curves cross
43
Figure 7: Market Equilibrium
E
HJ1.00
Rs3.00
D
S
50,000 75,00025,000
Excess Demand
4. until price reaches its equilibrium value of Rs3.00 .
2. causes the price to rise . . .
3. shrinking the excess demand . . .
1. At a price of Rs1.00 per bottle an excess demand of 50,000 bottles . . .
Number of Bottles per Month
Price per Bottle
44
Excess Demand
Excess demand– At a given price, the excess of quantity
demanded over quantity supplied
Price of the good will rise as buyers compete with each other to get more of the good than is available
45
Figure 8: Excess Supply and Price Adjustment
3. shrinking the excess supply . . .
K L
E3.00
D
S
Rs5.00
50,00035,000 65,000
Excess Supply at Rs5.00
2. causes the price to drop,
4. until price reaches its equilibrium value of Rs3.00.
Number of Bottles per Month
Price per Bottle
1. At a price of Rs5.00 per bottle an excess supply of 30,000 bottles . . .
46
Excess Supply
Excess Supply– At a given price, the excess of quantity supplied
over quantity demanded
Price of the good will fall as sellers compete with each other to sell more of the good than buyers want
47
Solve for Equilibrium Algebraically
Suppose that demand is given by the equation , where is quantity demanded, P is the price of the good. Supply is given by where is quantity supplied.
What is the equilibrium price and quantity?
PQD 10140
PQS 580
DQ
sQ
48
Income Rises: What Happens When Things Change
Income rises, causing an increase in demand– Rightward shift in the demand curve causes
rightward movement along the supply curve– Equilibrium price and equilibrium quantity
both rise
Shift of one curve causes a movement along the other curve to new equilibrium point
49
Figure 9
1. An increase in demand . . .E
F'
3.00
D1
D2
S
Rs4.00
50,000 60,000
3. to a new equilibrium.
5. and equilibrium quantity increases too.
2. moves us along the supply curve . . .
Number of Bottles of Maple Syrup per Period
Price per Bottle
4. Equilibrium price increases
50
An Ice Storm Hits: What Happens When Things Change
An ice storm causes a decrease in supply– Weather is a shift variable for supply curve
• Any change that shifts the supply curve leftward in a market will increase the equilibrium price
– And decrease the equilibrium quantity in that market
51
Figure 10: A Shift of Supply and A New Equilibrium
E'
E3.00
D
Rs5.00
50,00035,000
S2 S1
Number of Bottles
Price per Bottle
52
Using Supply and Demand: The Invasion of Kuwait
Why did Iraq’s invasion of Kuwait cause the price of oil to rise?– Immediately after the invasion, United States
led a worldwide embargo on oil from both Iraq and Kuwait
– A significant decrease in the oil industry’s productive capacity caused a shift in the supply curve to the left
• Price of oil increased
53
Figure 12: The Market For Oil
P2
D
E'
P1E
Q2 Q1
S2
S1
Barrels of Oil
Price per Barrel of Oil
54
Using Supply and Demand: The Invasion of Kuwait
Why did the price of natural gas rise as well?– Oil is a substitute for natural gas– Rise in the price of a substitute increases
demand for a good– Rise in price of oil caused demand curve for
natural gas to shift to the right• Thus, the price of natural gas rose
55
Figure 13: The Market For Natural Gas
Cubic Feet of Natural Gas
Price per Cubic Foot of Natural
Gas
P4
P3
F
Q3 Q4
S
D2
F'
D1
56
Figure 11: Changes in the Market for Handheld PCs
1. An increase in supply . . .
2. and a decrease in demand . . .
5. and quantity decreased as well.
A
BRs400
D2003
S2002
S2003
D2002
Rs500
2.45 3.33 Millions of Handheld PCs per Quarter
Price per Handheld
PC
4. Price decreased . . .
3. moved the market to a new equilibrium.
57
Both Curves Shift
When just one curve shifts (and we know the direction of the shift) we can determine the direction that both equilibrium price and quantity will move
When both curves shift (and we know the direction of the shifts) we can determine the direction for either price or quantity—but not both– Direction of the other will depend on which curve shifts
by more
58
The Three Step Process
Key Step 1—Characterize the Market– Decide which market or markets best suit problem
being analyzed and identify decision makers (buyers and sellers) who interact there
Key Step 2—Find the Equilibrium– Describe conditions necessary for equilibrium in the
market, and a method for determining that equilibrium
Key Step 3—What Happens When Things Change– Explore how events or government polices change
market equilibrium
59
Example: rental apartment
Example: problem 4, chapter 3 in textbook.
Demand & Supply Diagram Equilibrium P & Q Why Rs1000 can not be
equilibrium? Effects from a tornado
destroying some apartments.
rent(Rs)quantity demanded
quantity supplied
800 30 10
1000 25 14
1200 22 17
1400 19 19
1600 17 21
1800 15 22
60
Demand for two bedroom rental apartment
61
Summaries Through the study of the chapter, you will be able to Characterize a market. Use a demand schedule and a demand curve to demonstrate the law of
demand. Explain the difference between a change in demand (shift of the
curve) and a change in quantity demanded (movement along the curve).
List the factors that will lead to a change in demand, and give examples of each.
Similar analysis for supply side. Explain how equilibrium price and quantity are determined in a
competitive market. Explain what will happen in a competitive market after a shift in the
supply curve, the demand curve, or both. Describe the three steps economists take to answer almost any
question about the economy.