1. 6
Elasticity
Both the elasticity coefficient and the total revenue test for measuring price elasticity of demand are presented in the chapter. The text attempts to sharpen students’ ability to estimate price elasticity by discussing its major determinants. The chapter reviews a number of applications and presents empirical estimates for a variety of products. Cross- and income elasticities of demand and price elasticity of supply are also addressed.
McGraw-Hill/Irwin
Copyright © 2012 by The McGraw-Hill Companies, Inc. All rights reserved.

2. Price Elasticity of Demand
Measures buyers’ responsiveness to price changes
Formula for price elasticity of demand
Ed =
Percentage Change in Quantity
Demanded of Product X
Law of demand tells us that consumers will respond to a price decrease by buying more of a product (other things remaining constant), but it does not tell us how much more. The degree of responsiveness or sensitivity of consumers to a change in price is measured by the concept of price elasticity of demand.
If demand is elastic, there is a large change in quantity demanded even when price changes by a small amount. When demand is inelastic, there is a very small change in quantity demanded even when there is a large change in price.
Percentage Change in Price
of Product X
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3. Price Elasticity of Demand Formula
Eliminate the minus sign
Easier to compare elasticities
Absolute changes depend on the choice of units. For example, a change in the price of a $10,000 car by $1 is very different than a change in the price a of $1 can of beer by $1. The auto’s price is rising by a fraction of a percent while the beer’s price is rising 100 percent.
Percentages also make it possible to compare elasticities of demand for different products.
Because of the inverse relationship between price and quantity demanded, the actual elasticity of demand will be a negative number. However, we ignore the minus sign and use absolute value. This makes it less confusing to interpret the elasticity coefficient.
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4. Price Elasticity of Demand
Elastic demand, Ed > 1
Sensitive to price changes
Large change in quantity for small price change
Inelastic demand, Ed < 1
Insensitive to price changes
Small change in quantity for large price change
Unit elastic demand, Ed = 1
Equal changes in quantity and price
If demand is elastic, there is a large change in quantity demanded even when price changes by a small amount. When demand is inelastic, there is a very small change in quantity demanded even when there is a large change in price. When the elasticity coefficient is greater than 1, it means that the percentage change in quantity demanded is greater than the percentage change in price (based on the formula), indicating that consumers are sensitive to the change in price so demand is elastic.
When the elasticity coefficient is less than 1, the percentage change in quantity demanded is less than the percentage change in price (based on the formula), indicating that consumers are not very sensitive to price changes.
When the elasticity coefficient equals 1, this is a special case called unit elasticity. This means that the percentage change in price and the percentage change in quantity are exactly equal.
Perfectly inelastic demand means that consumers will buy exactly the same amount no matter how high or low the price. Perfectly elastic demand means that nothing will be purchased if there is any deviation from the current price.
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5. Perfectly inelastic demand
Extreme Cases P D1
Perfectly inelastic demand
(Ed = 0)
This extreme situation is called perfectly inelastic demand and it is very rare. The demand curve would be vertical and graphs as a line parallel to the vertical axis. The elasticity coefficient is 0. An example of a perfectly inelastic demand might be a diabetic’s demand for insulin.
Perfectly inelastic demand
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6. Extreme Cases Perfectly elastic demand P D2 Perfectly elastic demand
(Ed = ∞)
This extreme situation, in which a small price reduction would cause buyers to increase their purchases from zero to all that it is possible to obtain, is perfectly elastic demand, and the demand curve would be horizontal. The elasticity coefficient is infinite. An example of a perfectly elastic demand is a firm’s demand curve in a purely competitive industry who is unable to change the price.
Perfectly elastic demand
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7. Price Elasticity of Demand
Can not use slope to determine elasticity
Can use slope to determine relative elasticity.
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8. Total Revenue = Price X Quantity Inelastic demand Elastic demand
Total Revenue Test
Total Revenue = Price X Quantity
Inelastic demand
P and TR move in the same direction
Elastic demand
P and TR move in opposite directions
Unit elastic demand
TR doesn’t change when P changes
Total-revenue test is the easiest way to judge whether demand is elastic or inelastic. This test can be used in place of the elasticity formula, unless there is a need to determine the elasticity coefficient. The total revenue test is important to understand the relationship between price elasticity and total revenue.
Demand is inelastic if a decrease in price results in a fall in total revenue, or an increase in price results in a rise in total revenue.
Demand is elastic if a decrease in price results in a rise in total revenue, or if an increase in price results in a decline in total revenue.
Demand is unit elastic if total revenue does not change when the price changes.
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9. Total Revenue Test
Table 6.1 Price Elasticity of Demand for Movie Tickets as Measured by the Elasticity Coefficient and the Total-Revenue Test
(1)
Total Quantity of Tickets Demanded per Week, Thousands
(2)
Price per Ticket
(3)
Elasticity Coefficient (Ed)
(4)
Total Revenue
(1) X (2)
(5)
Total Revenue Test 1 $8
$8,000 2 7
5.00
14,000
Elastic 3 6
2.60
18,000 4 5
1.57
20,000
1.00
Unit Elastic
0.64
Inelastic
0.38 8
0.20
8,000
Notice that in the high price region, demand for movie tickets is elastic and revenues increase as price falls. Midway demand for movie tickets is unit elastic and revenues stay the same as price falls. In the low price region, elasticities of demand are inelastic and revenues fall as the price falls.
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10. Summary of Price Elasticity of Demand
Table 6.2 Price Elasticity of Demand: A Summary
Absolute Value of Elasticity Coefficient
Demand Is:
Description
Impact on Total Revenue of a:
Price Increase
Price Decrease
Greater than 1
(Ed > 1)
Elastic or relatively elastic
Qd changes by a larger percentage than does price
Total Revenue decreases
Total Revenue increases
Equal to 1
(Ed = 1)
Unit or unitary elastic
Qd changes by the same percentage as does price
Total revenue is unchanged
Total revenue
is unchanged
Less than 1
(Ed < 1)
Inelastic or relatively inelastic
Qd changes by a smaller percentage than does price
Total revenue increases
Total revenue decreases
This is a summary of the rules and concepts related to the elasticity of demand. This is an excellent table to study and help you prepare for the test. It’s a great summary of all of the different pieces to consider with elasticity and get an idea of how they fit together and change.
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11. Determinants of Elasticity of Demand
Substitutability
More substitutes, demand is more elastic
Proportion of Income
Higher proportion of income, demand is more elastic
Luxuries vs. Necessities
Luxury goods, demand is more elastic
Time
More time available, demand is more elastic
With more substitutes available, consumers have more alternative options so when there is a change in price, there is a greater percentage change in quantity demanded, making the demand more elastic. The broader the definition of the market, the more elastic the demand. With a more narrow definition of the market, demand is more inelastic.
The greater the proportion of income needed to buy the good the more elastic the demand. Consumers will be more sensitive to changes in prices because the price change can result in thousands of dollars difference.
Since luxuries are goods that consumers can go without, they will change the amount they purchase by a greater amount even if the price changes by a small amount.
It takes time to alter the amount being purchased, so the more time available, the more elastic the demand. A person doing their Christmas shopping on Christmas eve has a very inelastic demand because he/she doesn’t have the time to look around for alternative purchases.
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12. Price Elasticity of Demand
Table Selected Price Elasticities of Demand
Product or Service
Price Elasticity of Demand (Ed)
Newspapers
.10
Milk
.63
Electricity (household)
.13
Household appliances
Bread
.15
Liquor
.70
MLB Tickets
.23
Movies
.87
Telephone Service
.26
Beer
.90
Cigarettes
.25
Shoes
.91
Sugar
.30
Motor vehicles
1.14
Medical Care
.31
Beef
1.27
Eggs
.32
China, glassware
1.54
Legal Services
.37
Residential land
1.60
Automobile repair
.40
Restaurant meals
2.27
Clothing
.49
Lamb and mutton
2.65
Gasoline
.60
Fresh peas
2.83
Some of the elasticities of the goods in this table are surprising. Use the determinants of demand to discuss why major league baseball tickets are not only inelastic, but they are more inelastic than gasoline. What makes newspapers, movies, and beer inelastic?
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13. Decriminalization of Illegal Drugs
Applications of Ed
Large Crop Yields
Inelastic demand, lower total revenue
Excise Taxes
Inelastic demand, more total revenue
Decriminalization of Illegal Drugs
Decrease street crime
Large crop yields mean that the supply of crops increases and shifts to the right. When this occurs the equilibrium price falls. Since demand is inelastic, the lower price actually leads to lower revenue for farmers. Farmers are worse off when there is a large crop yield.
When government wants to impose taxes on goods, it is important for them to understand the elasticity of demand for the good. If they place a tax on a good with an inelastic demand, the higher price won’t decrease the quantity purchased by much thereby increasing the amount of tax revenue that government collects.
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14. Price Elasticity of Supply
Measures sellers’ responsiveness to price changes
Elastic supply (Es > 1 ), producers are responsive to price changes
Inelastic supply (Es < 1), producers are not responsive to price changes
We know that at higher prices, firms are willing and able to produce more whereas at lower prices, firms are willing and able to produce less. Price elasticity of supply measures how sensitive firms are to price changes. This means that even for small changes in price, firms will greatly alter the quantity being produced. On the other hand, when supply is inelastic, this means that the firm is unresponsive to price changes and therefore will not change the amount being produced by much even when the change in price is large.
We use percentages so it doesn’t matter which unit of measure we are using. The concept of price elasticity also applies to supply. The elasticity formula is the same as that for demand, but we must substitute the word “supplied” for the word “demanded” everywhere in the formula. Just like with price elasticity of demand, we will compute the price elasticity of supply using the midpoint formula.
Percentage Change in Quantity
Supplied of Product X
Percentage Change in Price
of Product X
Es =
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15. Price Elasticity of Supply
Time is primary determinant of elasticity of supply
Time periods considered
Immediate Market period
Can’t adjust any resources
Short Run
Able to adjust some resources
Long Run
Able to adjust all resources
The ease of shifting resources between alternative uses is very important in price elasticity of supply because it will determine how much flexibility a producer has to adjust his/her output to a change in the price. The degree of flexibility, and therefore the time period, will be different in different industries.
The market period means that there is no time to adjust output in response to a price change. Some industries may not have a market period.
The short run means that there is enough time to adjust output by increasing or decreasing the variable inputs but not the fixed inputs.
The long run means that there is enough time to adjust output by increasing or decreasing all inputs.
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16. Applications of Elasticity of Supply
Antiques
Inelastic supply
Reproductions
More elastic supply
Volatile gold prices
Antiques and other non-reproducible commodities have an inelastic supply, sometimes the supply is perfectly inelastic. This makes their prices highly susceptible to fluctuations in demand. The more inelastic the supply, the greater the changes in price when demand changes.
Reproductions on the other hand, have a much more elastic supply so the prices tend to remain lower even when there is an increase in demand.
Gold prices are volatile because the supply of gold is highly inelastic, and unstable demand from speculation causes prices to fluctuate significantly
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17. Cross Elasticity of Demand
Measures responsiveness of sales to change in the price of another good
Substitutes – positive sign
Complements – negative sign
Independent goods - zero
Percentage change in quantity demanded of product X
Ex,y =
Percentage change in price of product Y
We know that if the price of Pepsi increases it not only impacts the quantity of Pepsi that is purchased, but it also impacts the quantity of related goods that are purchased. Cross elasticity of demand refers to the effect of a change in a product’s price on the quantity demanded for another product. If the goods are substitutes, they will have a positive cross elasticity of demand since the change in the price of one good and the change in the demand for its substitute move in the same direction. If the goods are complements, they will have a negative cross elasticity of demand since the change in the price of one good and the demand for its complement move in opposite directions.
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18. Income Elasticity of Demand
Measures responsiveness of buyers to changes in income
Normal goods – positive sign
Inferior goods – negative sign
Percentage change
in quantity demanded
Ei =
Percentage change in income
Income elasticity of demand refers to the percentage change in quantity demanded that results from some percentage change in consumer incomes.
A positive income elasticity indicates a normal or superior good.
A negative income elasticity indicates an inferior good.
Those industries that are income elastic will expand at a higher rate as the economy grows.
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