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ECON649/ECON991
Lecture 2
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Chapter 3
The supply and demand model
Learning objectives
• Define demand and represent it graphically using a demand
curve
• Explain, and distinguish between, movements along the
demand curve and shifts of the demand curve
• Define supply and represent it graphically using a supply curve
• Explain, and distinguish between, movements along the
supply curve and shifts of the supply curve
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Learning objectives
• Combine supply and demand, and use this model to
determine equilibrium price and equilibrium quantity
• Use the supply and demand model to explain and predict the
effects of changes in the market
• Discuss the consequences of price floors and price ceilings.
Introduction
• In a market economic system, the information that people
need to make decisions is provided by prices.
• The price of any product is a measure of the combined
preferences of consumers and the relative scarcity of the
product.
• The model economists use to explain how prices are
determined in a market economy is called the supply and
demand model.
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Demand
• Demand is a relationship between two economic
variables:
1. The price of a particular good; and
2. The quantity of the good that consumers are willing to
buy at that price during a specific time period, all other
things being equal.
• Demand can be represented either numerically, with a
table, or graphically, with a curve.
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Demand
• Demand schedule: a tabular
representation of demand
showing the price and quantity
demanded for a particular
good, all other things being
equal.
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The demand curve
• Demand curve: a
graph of demand
showing the
downward‐
sloping
relationship
between price
and quantity
demanded.
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The law of demand
• The law of demand: price and quantity demanded are
negatively related – as price rises, quantity demanded falls
(ceteris paribus).
• Why does the demand curve slope downwards?
• There are two reasons:
1. The income effect; and
2. The substitution effect.
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The income effect
• If the price of bicycles falls, the ‘real income’ of consumers
increases even though their money income is unchanged.
• If the price of bicycles is $600, and a consumer has $1200
of income, his or her real income equals two bicycles.
• If the price of bicycles falls from $600 to $300, the
consumer’s real income has increased to four bicycles.
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The substitution effect
• If the price of bicycles rises, bicycles become more
expensive in comparison with other goods, and the
quantity demanded falls – people will switch to relatively
cheaper substitute goods.
• The income effect and the substitution effect work
together to explain the law of demand.
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Other factors affecting demand
• Price is not the only thing that affects the quantity of a
good that people plan to buy.
• The other ceteris paribus factors are:
– consumer preferences
– consumers’ information
– consumers’ income
– The number of consumers in the market
– consumers’ expectations of the future
– the prices of closely related goods.
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Other factors affecting demand
• Changes in these ‘other’ factors cause the demand to
shift.
• The demand curve can shift in two ways:
1. An increase in demand causes the demand curve to
shift to the right; and
2. A decrease in demand causes the demand curve to
shift to the left.
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An increase in demand
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Consumers’ preferences
• Consumers’ preferences or tastes for a product (relative
to another product) will change with the amount they
purchase at a given price.
• Example: the increasing availability of bike lanes leading
to an increase in the demand for bicycles.
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Consumers’ information
• New information available to consumers can result in a
change in the quantity of a good that consumers buy,
even though the price does not change.
• Example: information about the effects of trans fats might
have reduced the demand for French fries and increased
the demand for olive oil.
Which demand curve would shift to the right?
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Consumers’ incomes
• An increase in income increases the demand for most
goods.
• Normal goods: goods for which demand increases when
consumers’ income rises and decreases when consumers’
income falls.
• Examples:
• shoes
• clothing
• jewellery.
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Consumers’ incomes
• Inferior goods: goods for which demand decreases when
consumers’ income rises and increases when consumers’
income falls.
• Examples:
• low‐quality products
• ‘home brand’ products.
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Number of consumers in the market
• More consumers in the market will likely result in a larger
demand for the good or service, while fewer consumers
will likely result in a smaller demand for the good or
service.
• Example: as the number of older people in the population
increases, the demand for nursing homes is expected to
increase.
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Consumers’ expectations of future
prices
• Expectations of higher future prices will increase demand
now. Expectations of lower future prices will decrease
demand now.
• Example: expectations of higher petrol prices in the future
tends to make individuals fill up now.
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Prices of closely related goods
• Substitute: a good that has many of the same
characteristics as, and can be used in place of, another
good.
• Examples:
• Coke is a substitute for Pepsi.
• margarine can be substituted for butter.
• downloaded music is a substitute for music CDs.
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Prices of closely related goods
• Complement: a good that is consumed or used together
with another good.
• Examples:
• a bicycle helmet is a complement to a bicycle.
• petrol is a complement to SUVs.
• sugar is a complement to coffee.
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Prices of closely related goods
• If two goods are complements, then an increase in the
price of one good will result in a decrease in the demand
for the other good.
• If two goods are substitutes, then an increase in the price
of one good will result in an increase in the demand for
the other good.
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Movements along versus shifts of
the demand curve
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• It is very
important not
to confuse
shifts of the
demand curve
with
movements
along the
demand curve.
Supply
• Supply is a relationship between two economic variables:
1. the price of a particular good; and
2. the quantity of the good that businesses are willing to sell at
that price during a specific time period, all other things
being equal.
• Supply can be represented either numerically, with a
table, or graphically, with a curve.
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Supply
• Supply schedule:
a tabular
representation of
the supply curve.
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The supply curve
• Supply curve: the
graph of supply
showing the upward
relationship between
price and quantity
supplied.
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The law of supply
• The law of supply says that the price and the quantity
supplied are positively related. Why?
1. Profit incentive – as price rises, businesses will have a
greater incentive to increase quantity supplied.
2. Higher costs – as output increases, marginal costs rise.
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Shifts in supply
• The supply curve is drawn assuming that all other things
are equal, except the price of the good. If any one of these
other factors changes, then the supply curve shifts.
• What are these factors?
• technology
• prices of inputs used in production
• the number of businesses in the market
• the expected future selling price
• government taxes, subsidies and regulations.
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Shifts in supply
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Technology
• Anything that changes the amount that a business can
produce with a given amount of inputs can be considered
a change in technology. Improvements in technology will
correspond with an increase in supply.
• The supply curve would shift to the _______.
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The price of inputs used in
production
• More expensive inputs (raw materials, land and capital)
increases the cost of production of goods and services,
and may force the business to sell less at a given price.
• This would shift the supply curve to the _____.
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The number of businesses in the
market
• If the number of firms in the market increases, the supply
curve shifts to the right.
• If the number of firms in the market decreases, the supply
curve shifts to the left.
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Expectations of future prices
• Expectations of higher selling prices in the future will
decrease the supply today as businesses decide to sell
more in the future, when prices are higher – the supply
curve will shift to the _____ .
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Government taxes, subsidies and
regulations
• An increases in taxes (payments by businesses to the
government) or a decrease in subsidies (payment by the
government to businesses) will decrease supply – the
supply curve will shift to the ______.
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Government taxes, subsidies and
regulations
• Regulations: government policies or rules that control a
business’ behavior. These regulations can affect a
business’ cost of production and thereby affect supply.
• Example: government requirements that food vendors
pass sanitary inspection will reduce the number of
vendors and decrease supply – the supply curve will shift
to the ______ .
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Movements along versus shifts of
the supply curve
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• It is very important
not to confuse shifts
of the supply curve
with movements
along the supply
curve.
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Market equilibrium
• To determine the market price, we combine the demand
schedule with the supply schedule.
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Market equilibrium
• Market equilibrium: the situation in which the price
equals the equilibrium price, and the quantity traded
equals the equilibrium quantity.
• Refer to Table 3.3. What is the equilibrium price and
quantity?
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Market equilibrium
• Shortage (excess demand): a situation in which the quantity
demanded is greater than the quantity supplied. This occurs
when the price in the market is below the equilibrium price.
• Surplus (excess supply): a situation in which the quantity
supplied is greater than the quantity demanded. This occurs
when the current price in the market is above the equilibrium
price.
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Finding the equilibrium with a supply and
demand diagram
• The equilibrium price
occurs at the
intersection of the
supply curve and the
demand curve.
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Finding the equilibrium with a supply
and demand diagram
• If the price is below the equilibrium, a shortage occurs,
causing the price to increase until the price reaches
equilibrium.
• If the price is above the equilibrium, a surplus occurs,
causing the price to decrease until the price reaches
equilibrium.
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A change in the market
• An increase in demand will shift the demand curve to the
right, resulting in a higher equilibrium price and quantity.
• A decrease in demand will shift the demand curve to the
left, resulting in a lower equilibrium price and quantity.
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A change in the market
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A change in the market
• An increase in supply will shift the supply curve to the
right, resulting in a lower equilibrium price and a higher
equilibrium quantity.
• A decrease in supply will shift the supply curve to the left,
resulting in a higher equilibrium price and a lower
equilibrium quantity.
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A change in the market
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A change in the market
• What happens to the equilibrium price and quantity if both
curves shift – if, for example, both demand and supply
increase?
• The equilibrium quantity will increase, but the equilibrium
price may rise, fall or stay the same.
• To determine what happens to price, we need to know which
curve will shift more. If demand increases more than supply,
then price will rise; if supply increases more than demand,
then price will fall.
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A change in the market
• Predict what will happen to equilibrium price and quantity in
each of the following scenarios.
1. Demand increases and supply decreases
2. Demand decreases and supply decreases
3. Demand decreases and supply increases.
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Application
• The demand for large‐screen televisions has been increasing
each year, and yet their prices have been falling!
• If demand increases, all other things being equal, then prices
should rise. But supply has also been increasing, due to
improving technology reducing production costs.
• If supply increases faster than demand, then prices will fall.
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Interference with market prices
• Price control: a government control or regulation that sets
or limits the price to be charged for a particular good. Such
controls are typically imposed because the government is
not satisfied with the equilibrium price.
• Two broad types of price controls:
• price floor
• price ceiling.
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Price ceilings
• Price ceiling: a government price control that sets the
maximum allowable price for a good or a service in the
belief that the equilibrium price is too high.
• Example: rent control: a government price control that
sets a maximum allowable rent to a house or an
apartment.
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Price ceilings
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Side effects of price ceilings
• If the government sets a price ceiling below the
equilibrium price, a shortage will result.
• Ways we deal with persistent shortages:
• coupons
• long lines
• reduction in the quality of the good sold
• black markets.
• Are these effects good or bad?
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Price floors
• Price floor: a government price control that sets the
minimum allowable price for a good or a service in the
belief that the equilibrium price is too low.
• Example: Minimum wage: a wage per hour below which it
is illegal to pay workers.
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Price floors
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Side effects of price floors
• If the government sets a price floor above the equilibrium
price, a surplus will result.
• Dealing with surpluses:
– With agricultural products, the surpluses are
purchased by the government. Sometimes, the
government pays farmers not to produce.
– Minimum wages cause a surplus in labour
(unemployment). The government does not lower
wages to eliminate the surplus labour.
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Readings
• This week:
‐ Frost, L., Taylor, J., Weerapana, A. and
Schuwalow, P. (2013) Microeconomics: Principles
and Practice, Cengage Learning, Chapter 3.
• Next week:
‐ Frost, L., Taylor, J., Weerapana, A. and
Schuwalow, P. (2013) Microeconomics: Principles
and Practice, Cengage Learning, Chapters 4 & 5.
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