![© 2007 Thomson South-Western
The Midpoint Method: A Better Way to Calculate
Percentage Changes and Elasticities
• The midpoint formula is preferable when
calculating the price elasticity of demand
because it gives the same answer regardless of
the direction of the price change.
2 1 2 1
2 1 2 1
( )/[( )/ 2]
Price elasticity of demand =
( )/[( )/ 2]
Q Q Q Q
P P P P
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05_4E - Elasticity and Its Application.ppt
- 1. © 2007 Thomson South-Western
- 2. © 2007 Thomson South-Western Elasticity . . . • … allows us to analyze supply and demand with greater precision. • … is a measure of how much buyers and sellers respond to changes in market conditions
- 3. © 2007 Thomson South-Western THE ELASTICITY OF DEMAND • The price elasticity of demand is a measure of how much the quantity demanded of a good responds to a change in the price of that good. • When we talk about elasticity, that responsiveness is always measured in percentage terms. • Specifically, the price elasticity of demand is the percentage change in quantity demanded due to a percentage change in the price.
- 4. © 2007 Thomson South-Western The Price Elasticity of Demand and Its Determinants • Availability of Close Substitutes • Necessities versus Luxuries • Definition of the Market • Time Horizon
- 5. © 2007 Thomson South-Western The Price Elasticity of Demand and Its Determinants • Demand tends to be more elastic: • the larger the number of close substitutes. • if the good is a luxury. • the more narrowly defined the market. • the longer the time period.
- 6. © 2007 Thomson South-Western Computing the Price Elasticity of Demand • The price elasticity of demand is computed as the percentage change in the quantity demanded divided by the percentage change in price. Price elasticity of demand = Percentage change in quantity demanded Percentage change in price
- 7. © 2007 Thomson South-Western Computing the Price Elasticity of Demand • Example: If the price of an ice cream cone increases from $2.00 to $2.20 and the amount you buy falls from 10 to 8 cones, then your elasticity of demand would be calculated as: ( ) ( . . ) . 10 8 10 100 2 20 2 00 2 00 100 20% 10% 2 Price elasticity of demand = Percentage change in quantity demanded Percentage change in price
- 8. © 2007 Thomson South-Western The Midpoint Method: A Better Way to Calculate Percentage Changes and Elasticities • The midpoint formula is preferable when calculating the price elasticity of demand because it gives the same answer regardless of the direction of the price change. 2 1 2 1 2 1 2 1 ( )/[( )/ 2] Price elasticity of demand = ( )/[( )/ 2] Q Q Q Q P P P P
- 9. © 2007 Thomson South-Western The Midpoint Method: A Better Way to Calculate Percentage Changes and Elasticities • Example: If the price of an ice cream cone increases from $2.00 to $2.20 and the amount you buy falls from 10 to 8 cones, then your elasticity of demand, using the midpoint formula, would be calculated as: (10 8) 22% (10 8)/ 2 2.32 (2.20 2.00) 9.5% (2.00 2.20)/ 2
- 10. © 2007 Thomson South-Western The Variety of Demand Curves • Inelastic Demand • Quantity demanded does not respond strongly to price changes. • Price elasticity of demand is less than one. • Elastic Demand • Quantity demanded responds strongly to changes in price. • Price elasticity of demand is greater than one.
- 11. © 2007 Thomson South-Western Computing the Price Elasticity of Demand Demand is price elastic. $5 4 Demand Quantity 100 0 50 3 percent 22 percent 67 5.00)/2 (4.00 5.00) (4.00 50)/2 (100 50) (100 ED Price
- 12. © 2007 Thomson South-Western The Variety of Demand Curves • Perfectly Inelastic • Quantity demanded does not respond to price changes. • Perfectly Elastic • Quantity demanded changes infinitely with any change in price. • Unit Elastic • Quantity demanded changes by the same percentage as the price.
- 13. © 2007 Thomson South-Western The Variety of Demand Curves • Because the price elasticity of demand measures how much quantity demanded responds to the price, it is closely related to the slope of the demand curve. • But it is not the same thing as the slope!
- 14. © 2007 Thomson South-Western Figure 1 The Price Elasticity of Demand (a) Perfectly Inelastic Demand: Elasticity Equals 0 $5 4 Quantity Demand 100 0 1. An increase in price . . . 2. . . . leaves the quantity demanded unchanged. Price
- 15. © 2007 Thomson South-Western Figure 1 The Price Elasticity of Demand (b) Inelastic Demand: Elasticity Is Less Than 1 Quantity 0 $5 90 Demand 1. A 22% increase in price . . . Price 2. . . . leads to an 11% decrease in quantity demanded. 4 100
- 16. © 2007 Thomson South-Western Figure 1 The Price Elasticity of Demand 2. . . . leads to a 22% decrease in quantity demanded. (c) Unit Elastic Demand: Elasticity Equals 1 Quantity 4 100 0 Price $5 80 1. A 22% increase in price . . . Demand
- 17. © 2007 Thomson South-Western Figure 1 The Price Elasticity of Demand (d) Elastic Demand: Elasticity Is Greater Than 1 Demand Quantity 4 100 0 Price $5 50 1. A 22% increase in price . . . 2. . . . leads to a 67% decrease in quantity demanded.
- 18. © 2007 Thomson South-Western Figure 1 The Price Elasticity of Demand (e) Perfectly Elastic Demand: Elasticity Equals Infinity Quantity 0 Price $4 Demand 2. At exactly $4, consumers will buy any quantity. 1. At any price above $4, quantity demanded is zero. 3. At a price below $4, quantity demanded is infinite.
- 19. © 2007 Thomson South-Western Total Revenue and the Price Elasticity of Demand • Total revenue is the amount paid by buyers and received by sellers of a good. • Computed as the price of the good times the quantity sold. Q P TR
- 20. © 2007 Thomson South-Western Figure 2 Total Revenue Demand Quantity Q P 0 Price P × Q = $400 (revenue) $4 100 When the price is $4, consumers will demand 100 units, and spend $400 on this good.
- 21. © 2007 Thomson South-Western Elasticity and Total Revenue along a Linear Demand Curve • With an inelastic demand curve, an increase in price leads to a decrease in quantity that is proportionately smaller. Thus, total revenue increases.
- 22. © 2007 Thomson South-Western Figure 3 How Total Revenue Changes When Price Changes: Inelastic Demand Demand Quantity 0 Price Revenue = $100 Quantity 0 Price Revenue = $240 Demand $1 100 $3 80 An Increase in price from $1 to $3 … … leads to an Increase in total revenue from $100 to $240
- 23. © 2007 Thomson South-Western Elasticity and Total Revenue along a Linear Demand Curve • With an elastic demand curve, an increase in the price leads to a decrease in quantity demanded that is proportionately larger. Thus, total revenue decreases.
- 24. © 2007 Thomson South-Western Figure 3 How Total Revenue Changes When Price Changes: Elastic Demand Demand Quantity 0 Price Revenue = $200 $4 50 Demand Quantity 0 Price Revenue = $100 $5 20 An Increase in price from $4 to $5 … … leads to an decrease in total revenue from $200 to $100 Note that with each price increase, the Law of Demand still holds – an increase in price leads to a decrease in the quantity demanded. It is the change in TR that varies!
- 25. © 2007 Thomson South-Western Elasticity of a Linear Demand Curve
- 26. © 2007 Thomson South-Western 0 2 6 4 10 8 12 14 2 1 4 3 5 6 $7 Demand is elastic; demand is responsive to changes in price. Demand is inelastic; demand is not very responsive to changes in price. When price increases from $4 to $5, TR declines from $24 to $20. When price increases from $2 to $3, TR increases from $20 to $24. Elasticity is > 1 in this range. Elasticity is < 1 in this range. Price Quantity Figure 4 Elasticity of a Linear Demand Curve
- 27. © 2007 Thomson South-Western Other Demand Elasticities • Income Elasticity of Demand • Income elasticity of demand measures how much the quantity demanded of a good responds to a change in consumers’ income. • It is computed as the percentage change in the quantity demanded divided by the percentage change in income.
- 28. © 2007 Thomson South-Western Other Demand Elasticities • Computing Income Elasticity Income elasticity of demand = Percentage change in quantity demanded Percentage change in income Remember, all elasticities are measured by dividing one percentage change by another
- 29. © 2007 Thomson South-Western Other Demand Elasticities • Income Elasticity • Types of Goods • Normal Goods • Inferior Goods • Higher income raises the quantity demanded for normal goods but lowers the quantity demanded for inferior goods.
- 30. © 2007 Thomson South-Western Other Demand Elasticities • Income Elasticity • Goods consumers regard as necessities tend to be income inelastic • Examples include food, fuel, clothing, utilities, and medical services. • Goods consumers regard as luxuries tend to be income elastic. • Examples include sports cars, furs, and expensive foods.
- 31. © 2007 Thomson South-Western Other Demand Elasticities • Cross-price elasticity of demand • A measure of how much the quantity demanded of one good responds to a change in the price of another good, computed as the percentage change in quantity demanded of the first good divided by the percentage change in the price of the second good 2 good of price in %change 1 good of demanded quantity in %change demand of elasticity price - Cross
- 32. © 2007 Thomson South-Western THE ELASTICITY OF SUPPLY • Price elasticity of supply is a measure of how much the quantity supplied of a good responds to a change in the price of that good. • Price elasticity of supply is the percentage change in quantity supplied resulting from a percentage change in price.
- 33. © 2007 Thomson South-Western Figure 5 The Price Elasticity of Supply (a) Perfectly Inelastic Supply: Elasticity Equals 0 $5 4 Supply Quantity 100 0 1. An increase in price . . . 2. . . . leaves the quantity supplied unchanged. Price
- 34. © 2007 Thomson South-Western Figure 5 The Price Elasticity of Supply (b) Inelastic Supply: Elasticity Is Less Than 1 110 $5 100 4 Quantity 0 1. A 22% increase in price . . . Price 2. . . . leads to a 10% increase in quantity supplied. Supply
- 35. © 2007 Thomson South-Western Figure 5 The Price Elasticity of Supply (c) Unit Elastic Supply: Elasticity Equals 1 125 $5 100 4 Quantity 0 Price 2. . . . leads to a 22% increase in quantity supplied. 1. A 22% increase in price . . . Supply (If SUPPLY is unit elastic and linear, it will begin at the origin.)
- 36. © 2007 Thomson South-Western Figure 5 The Price Elasticity of Supply (d) Elastic Supply: Elasticity Is Greater Than 1 Quantity 0 Price 1. A 22% increase in price . . . 2. . . . leads to a 67% increase in quantity supplied. 4 100 $5 200 Supply
- 37. © 2007 Thomson South-Western Figure 5 The Price Elasticity of Supply (e) Perfectly Elastic Supply: Elasticity Equals Infinity Quantity 0 Price $4 Supply 3. At a price below $4, quantity supplied is zero. 2. At exactly $4, producers will supply any quantity. 1. At any price above $4, quantity supplied is infinite.
- 38. © 2007 Thomson South-Western The Price Elasticity of Supply and Its Determinants • Ability of sellers to change the amount of the good they produce. • Beach-front land is inelastic. • Books, cars, or manufactured goods are elastic. • Time period • Supply is more elastic in the long run.
- 39. © 2007 Thomson South-Western Computing the Price Elasticity of Supply • The price elasticity of supply is computed as the percentage change in the quantity supplied divided by the percentage change in price. Price elasticity of supply = Percentage change in quantity supplied Percentage change in price
- 40. © 2007 Thomson South-Western THREE APPLICATIONS OF SUPPLY, DEMAND, AND ELASTICITY • Can good news for farming be bad news for farmers? • What happens to wheat farmers and the market for wheat when university agronomists discover a new wheat hybrid that is more productive than existing varieties?
- 41. © 2007 Thomson South-Western Can Good News for Farming Be Bad News for Farmers? • Examine whether the supply or demand curve shifts. • Determine the direction of the shift of the curve. • Use the supply-and-demand diagram to see how the market equilibrium changes.
- 42. © 2007 Thomson South-Western Figure 7 An Increase in Supply in the Market for Wheat Quantity of Wheat 0 Price of Wheat 3. . . . and a proportionately smaller increase in quantity sold. As a result, revenue falls from $300 to $220. Demand S1 S2 2. . . . leads to a large fall in price . . . 1. When demand is inelastic, an increase in supply . . . 2 110 $3 100
- 43. © 2007 Thomson South-Western Compute the Price Elasticity of Demand When There Is a Change in Supply ED 100 110 100 110 2 300 2 00 300 2 00 2 0 095 0 4 0 24 ( ) / . . ( . . ) / . . . Demand is inelastic.
- 44. © 2007 Thomson South-Western Why Did OPEC Fail to Keep the Price of Oil High? • Supply and Demand can behave differently in the short run and the long run • In the short run, both supply and demand for oil are relatively inelastic • But in the long run, both are elastic • Production outside of OPEC • More conservation by consumers
- 45. © 2007 Thomson South-Western Does Drug Interdiction Increase or Decrease Drug-Related Crime? • Drug interdiction impacts sellers rather than buyers. • Demand is unchanged. • Equilibrium price rises although quantity falls. • Drug education impacts the buyers rather than sellers. • Demand is shifted. • Equilibrium price and quantity are lowered.
- 46. © 2007 Thomson South-Western Price of Drugs Quantity of Drugs Price of Drugs Quantity of Drugs Drug Interdiction Drug Education D2 D1 D1 S2 S1 S1 The demand for illegal drugs is inelastic. Interdiction shifts the supply, while education shifts the demand. In each case, the change in price is the same. But in one market the price goes up. And in the other it goes down. The changes in quantities (and TR) are remarkable. It is amazing how useful knowledge of elasticities can be! Figure 9 Policies to Reduce the Use of Illegal Drugs
- 47. Summary © 2007 Thomson South-Western • Price elasticity of demand measures how much the quantity demanded responds to changes in the price. • Price elasticity of demand is calculated as the percentage change in quantity demanded divided by the percentage change in price. – If a demand curve is elastic, total revenue falls when the price rises. – If it is inelastic, total revenue rises as the price rises.
- 48. Summary © 2007 Thomson South-Western • The income elasticity of demand measures how much the quantity demanded responds to changes in consumers’ income. • The cross-price elasticity of demand measures how much the quantity demanded of one good responds to the price of another good. • The price elasticity of supply measures how much the quantity supplied responds to changes in the price.
- 49. Summary © 2007 Thomson South-Western • In most markets, supply is more elastic in the long run than in the short run. • The price elasticity of supply is calculated as the percentage change in quantity supplied divided by the percentage change in price. • The tools of supply and demand can be applied in many different types of markets.