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Principles of Macroeconomics 2e

5.1 Price Elasticity of Demand and Price Elasticity of Supply

Principles of Macroeconomics 2e5.1 Price Elasticity of Demand and Price Elasticity of Supply
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  1. Preface
  2. 1 Welcome to Economics!
    1. Introduction
    2. 1.1 What Is Economics, and Why Is It Important?
    3. 1.2 Microeconomics and Macroeconomics
    4. 1.3 How Economists Use Theories and Models to Understand Economic Issues
    5. 1.4 How To Organize Economies: An Overview of Economic Systems
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
  3. 2 Choice in a World of Scarcity
    1. Introduction to Choice in a World of Scarcity
    2. 2.1 How Individuals Make Choices Based on Their Budget Constraint
    3. 2.2 The Production Possibilities Frontier and Social Choices
    4. 2.3 Confronting Objections to the Economic Approach
    5. Key Terms
    6. Key Concepts and Summary
    7. Self-Check Questions
    8. Review Questions
    9. Critical Thinking Questions
    10. Problems
  4. 3 Demand and Supply
    1. Introduction to Demand and Supply
    2. 3.1 Demand, Supply, and Equilibrium in Markets for Goods and Services
    3. 3.2 Shifts in Demand and Supply for Goods and Services
    4. 3.3 Changes in Equilibrium Price and Quantity: The Four-Step Process
    5. 3.4 Price Ceilings and Price Floors
    6. 3.5 Demand, Supply, and Efficiency
    7. Key Terms
    8. Key Concepts and Summary
    9. Self-Check Questions
    10. Review Questions
    11. Critical Thinking Questions
    12. Problems
  5. 4 Labor and Financial Markets
    1. Introduction to Labor and Financial Markets
    2. 4.1 Demand and Supply at Work in Labor Markets
    3. 4.2 Demand and Supply in Financial Markets
    4. 4.3 The Market System as an Efficient Mechanism for Information
    5. Key Terms
    6. Key Concepts and Summary
    7. Self-Check Questions
    8. Review Questions
    9. Critical Thinking Questions
    10. Problems
  6. 5 Elasticity
    1. Introduction to Elasticity
    2. 5.1 Price Elasticity of Demand and Price Elasticity of Supply
    3. 5.2 Polar Cases of Elasticity and Constant Elasticity
    4. 5.3 Elasticity and Pricing
    5. 5.4 Elasticity in Areas Other Than Price
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  7. 6 The Macroeconomic Perspective
    1. Introduction to the Macroeconomic Perspective
    2. 6.1 Measuring the Size of the Economy: Gross Domestic Product
    3. 6.2 Adjusting Nominal Values to Real Values
    4. 6.3 Tracking Real GDP over Time
    5. 6.4 Comparing GDP among Countries
    6. 6.5 How Well GDP Measures the Well-Being of Society
    7. Key Terms
    8. Key Concepts and Summary
    9. Self-Check Questions
    10. Review Questions
    11. Critical Thinking Questions
    12. Problems
  8. 7 Economic Growth
    1. Introduction to Economic Growth
    2. 7.1 The Relatively Recent Arrival of Economic Growth
    3. 7.2 Labor Productivity and Economic Growth
    4. 7.3 Components of Economic Growth
    5. 7.4 Economic Convergence
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  9. 8 Unemployment
    1. Introduction to Unemployment
    2. 8.1 How Economists Define and Compute Unemployment Rate
    3. 8.2 Patterns of Unemployment
    4. 8.3 What Causes Changes in Unemployment over the Short Run
    5. 8.4 What Causes Changes in Unemployment over the Long Run
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  10. 9 Inflation
    1. Introduction to Inflation
    2. 9.1 Tracking Inflation
    3. 9.2 How to Measure Changes in the Cost of Living
    4. 9.3 How the U.S. and Other Countries Experience Inflation
    5. 9.4 The Confusion Over Inflation
    6. 9.5 Indexing and Its Limitations
    7. Key Terms
    8. Key Concepts and Summary
    9. Self-Check Questions
    10. Review Questions
    11. Critical Thinking Questions
    12. Problems
  11. 10 The International Trade and Capital Flows
    1. Introduction to the International Trade and Capital Flows
    2. 10.1 Measuring Trade Balances
    3. 10.2 Trade Balances in Historical and International Context
    4. 10.3 Trade Balances and Flows of Financial Capital
    5. 10.4 The National Saving and Investment Identity
    6. 10.5 The Pros and Cons of Trade Deficits and Surpluses
    7. 10.6 The Difference between Level of Trade and the Trade Balance
    8. Key Terms
    9. Key Concepts and Summary
    10. Self-Check Questions
    11. Review Questions
    12. Critical Thinking Questions
    13. Problems
  12. 11 The Aggregate Demand/Aggregate Supply Model
    1. Introduction to the Aggregate Supply–Aggregate Demand Model
    2. 11.1 Macroeconomic Perspectives on Demand and Supply
    3. 11.2 Building a Model of Aggregate Demand and Aggregate Supply
    4. 11.3 Shifts in Aggregate Supply
    5. 11.4 Shifts in Aggregate Demand
    6. 11.5 How the AD/AS Model Incorporates Growth, Unemployment, and Inflation
    7. 11.6 Keynes’ Law and Say’s Law in the AD/AS Model
    8. Key Terms
    9. Key Concepts and Summary
    10. Self-Check Questions
    11. Review Questions
    12. Critical Thinking Questions
    13. Problems
  13. 12 The Keynesian Perspective
    1. Introduction to the Keynesian Perspective
    2. 12.1 Aggregate Demand in Keynesian Analysis
    3. 12.2 The Building Blocks of Keynesian Analysis
    4. 12.3 The Phillips Curve
    5. 12.4 The Keynesian Perspective on Market Forces
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
  14. 13 The Neoclassical Perspective
    1. Introduction to the Neoclassical Perspective
    2. 13.1 The Building Blocks of Neoclassical Analysis
    3. 13.2 The Policy Implications of the Neoclassical Perspective
    4. 13.3 Balancing Keynesian and Neoclassical Models
    5. Key Terms
    6. Key Concepts and Summary
    7. Self-Check Questions
    8. Review Questions
    9. Critical Thinking Questions
    10. Problems
  15. 14 Money and Banking
    1. Introduction to Money and Banking
    2. 14.1 Defining Money by Its Functions
    3. 14.2 Measuring Money: Currency, M1, and M2
    4. 14.3 The Role of Banks
    5. 14.4 How Banks Create Money
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  16. 15 Monetary Policy and Bank Regulation
    1. Introduction to Monetary Policy and Bank Regulation
    2. 15.1 The Federal Reserve Banking System and Central Banks
    3. 15.2 Bank Regulation
    4. 15.3 How a Central Bank Executes Monetary Policy
    5. 15.4 Monetary Policy and Economic Outcomes
    6. 15.5 Pitfalls for Monetary Policy
    7. Key Terms
    8. Key Concepts and Summary
    9. Self-Check Questions
    10. Review Questions
    11. Critical Thinking Questions
    12. Problems
  17. 16 Exchange Rates and International Capital Flows
    1. Introduction to Exchange Rates and International Capital Flows
    2. 16.1 How the Foreign Exchange Market Works
    3. 16.2 Demand and Supply Shifts in Foreign Exchange Markets
    4. 16.3 Macroeconomic Effects of Exchange Rates
    5. 16.4 Exchange Rate Policies
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  18. 17 Government Budgets and Fiscal Policy
    1. Introduction to Government Budgets and Fiscal Policy
    2. 17.1 Government Spending
    3. 17.2 Taxation
    4. 17.3 Federal Deficits and the National Debt
    5. 17.4 Using Fiscal Policy to Fight Recession, Unemployment, and Inflation
    6. 17.5 Automatic Stabilizers
    7. 17.6 Practical Problems with Discretionary Fiscal Policy
    8. 17.7 The Question of a Balanced Budget
    9. Key Terms
    10. Key Concepts and Summary
    11. Self-Check Questions
    12. Review Questions
    13. Critical Thinking Questions
    14. Problems
  19. 18 The Impacts of Government Borrowing
    1. Introduction to the Impacts of Government Borrowing
    2. 18.1 How Government Borrowing Affects Investment and the Trade Balance
    3. 18.2 Fiscal Policy and the Trade Balance
    4. 18.3 How Government Borrowing Affects Private Saving
    5. 18.4 Fiscal Policy, Investment, and Economic Growth
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  20. 19 Macroeconomic Policy Around the World
    1. Introduction to Macroeconomic Policy around the World
    2. 19.1 The Diversity of Countries and Economies across the World
    3. 19.2 Improving Countries’ Standards of Living
    4. 19.3 Causes of Unemployment around the World
    5. 19.4 Causes of Inflation in Various Countries and Regions
    6. 19.5 Balance of Trade Concerns
    7. Key Terms
    8. Key Concepts and Summary
    9. Self-Check Questions
    10. Review Questions
    11. Critical Thinking Questions
    12. Problems
  21. 20 International Trade
    1. Introduction to International Trade
    2. 20.1 Absolute and Comparative Advantage
    3. 20.2 What Happens When a Country Has an Absolute Advantage in All Goods
    4. 20.3 Intra-industry Trade between Similar Economies
    5. 20.4 The Benefits of Reducing Barriers to International Trade
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  22. 21 Globalization and Protectionism
    1. Introduction to Globalization and Protectionism
    2. 21.1 Protectionism: An Indirect Subsidy from Consumers to Producers
    3. 21.2 International Trade and Its Effects on Jobs, Wages, and Working Conditions
    4. 21.3 Arguments in Support of Restricting Imports
    5. 21.4 How Governments Enact Trade Policy: Globally, Regionally, and Nationally
    6. 21.5 The Tradeoffs of Trade Policy
    7. Key Terms
    8. Key Concepts and Summary
    9. Self-Check Questions
    10. Review Questions
    11. Critical Thinking Questions
    12. Problems
  23. A | The Use of Mathematics in Principles of Economics
  24. B | The Expenditure-Output Model
  25. Answer Key
    1. Chapter 1
    2. Chapter 2
    3. Chapter 3
    4. Chapter 4
    5. Chapter 5
    6. Chapter 6
    7. Chapter 7
    8. Chapter 8
    9. Chapter 9
    10. Chapter 10
    11. Chapter 11
    12. Chapter 12
    13. Chapter 13
    14. Chapter 14
    15. Chapter 15
    16. Chapter 16
    17. Chapter 17
    18. Chapter 18
    19. Chapter 19
    20. Chapter 20
    21. Chapter 21
  26. References
  27. Index
By the end of this section, you will be able to:
  • Calculate the price elasticity of demand
  • Calculate the price elasticity of supply

Both the demand and supply curve show the relationship between price and the number of units demanded or supplied. Price elasticity is the ratio between the percentage change in the quantity demanded (Qd) or supplied (Qs) and the corresponding percent change in price. The price elasticity of demand is the percentage change in the quantity demanded of a good or service divided by the percentage change in the price. The price elasticity of supply is the percentage change in quantity supplied divided by the percentage change in price.

We can usefully divide elasticities into three broad categories: elastic, inelastic, and unitary. An elastic demand or elastic supply is one in which the elasticity is greater than one, indicating a high responsiveness to changes in price. Elasticities that are less than one indicate low responsiveness to price changes and correspond to inelastic demand or inelastic supply. Unitary elasticities indicate proportional responsiveness of either demand or supply, as Table 5.1 summarizes.

If . . . Then . . . And It Is Called . . .
% change in quantity>% change in price% change in quantity>% change in price % change in quantity% change in price>1% change in quantity% change in price>1 Elastic
% change in quantity=% change in price% change in quantity=% change in price % change in quantity% change in price=1% change in quantity% change in price=1 Unitary
% change in quantity<% change in price% change in quantity<% change in price % change in quantity% change in price<1% change in quantity% change in price<1 Inelastic
Table 5.1 Elastic, Inelastic, and Unitary: Three Cases of Elasticity

Link It Up

Before we delve into the details of elasticity, enjoy this article on elasticity and ticket prices at the Super Bowl.

To calculate elasticity along a demand or supply curve economists use the average percent change in both quantity and price. This is called the Midpoint Method for Elasticity, and is represented in the following equations:

% change in quantity=Q2Q1Q2+ Q1/2 × 100% change in price=P2 P1P2+ P1/2 × 100 % change in quantity=Q2Q1Q2+ Q1/2 × 100% change in price=P2 P1P2+ P1/2 × 100

The advantage of the Midpoint Method is that one obtains the same elasticity between two price points whether there is a price increase or decrease. This is because the formula uses the same base (average quantity and average price) for both cases.

Calculating Price Elasticity of Demand

Let’s calculate the elasticity between points A and B and between points G and H as Figure 5.2 shows.

The graph shows a downward sloping line that represents the price elasticity of demand.
Figure 5.2 Calculating the Price Elasticity of Demand We calculate the price elasticity of demand as the percentage change in quantity divided by the percentage change in price.

First, apply the formula to calculate the elasticity as price decreases from $70 at point B to $60 at point A:

% change in quantity=3,0002,800(3,000+2,800)/2 × 100=2002,900 × 100=6.9% change in price=6070(60+70)/2 × 100=–1065 × 100=–15.4Price Elasticity of Demand=    6.9%–15.4%=0.45% change in quantity=3,0002,800(3,000+2,800)/2 × 100=2002,900 × 100=6.9% change in price=6070(60+70)/2 × 100=–1065 × 100=–15.4Price Elasticity of Demand=    6.9%–15.4%=0.45

Therefore, the elasticity of demand between these two points is     6.9%–15.4%    6.9%–15.4% which is 0.45, an amount smaller than one, showing that the demand is inelastic in this interval. Price elasticities of demand are always negative since price and quantity demanded always move in opposite directions (on the demand curve). By convention, we always talk about elasticities as positive numbers. Mathematically, we take the absolute value of the result. We will ignore this detail from now on, while remembering to interpret elasticities as positive numbers.

This means that, along the demand curve between point B and A, if the price changes by 1%, the quantity demanded will change by 0.45%. A change in the price will result in a smaller percentage change in the quantity demanded. For example, a 10% increase in the price will result in only a 4.5% decrease in quantity demanded. A 10% decrease in the price will result in only a 4.5% increase in the quantity demanded. Price elasticities of demand are negative numbers indicating that the demand curve is downward sloping, but we read them as absolute values. The following Work It Out feature will walk you through calculating the price elasticity of demand.

Work It Out

Finding the Price Elasticity of Demand

Calculate the price elasticity of demand using the data in Figure 5.2 for an increase in price from G to H. Has the elasticity increased or decreased?

Step 1. We know that:

Price Elasticity of Demand=% change in quantity% change in pricePrice Elasticity of Demand=% change in quantity% change in price

Step 2. From the Midpoint Formula we know that:

change in quantity=Q2Q1(Q2+Q1)/2 × 100change in price=P2P1(P2+P1)/2 × 100change in quantity=Q2Q1(Q2+Q1)/2 × 100change in price=P2P1(P2+P1)/2 × 100

Step 3. So we can use the values provided in the figure in each equation:

% change in quantity=1,6001,800(1,600+1,800)/2 × 100=–2001,700 × 100=–11.76% change in price=130120(130+120)/2 × 100=10125 × 100=8.0% change in quantity=1,6001,800(1,600+1,800)/2 × 100=–2001,700 × 100=–11.76% change in price=130120(130+120)/2 × 100=10125 × 100=8.0

Step 4. Then, we can use those values to determine the price elasticity of demand:

Price Elasticity of Demand=% change in quantity% change in price=–11.768=1.47Price Elasticity of Demand=% change in quantity% change in price=–11.768=1.47

Therefore, the elasticity of demand from G to is H 1.47. The magnitude of the elasticity has increased (in absolute value) as we moved up along the demand curve from points A to B. Recall that the elasticity between these two points was 0.45. Demand was inelastic between points A and B and elastic between points G and H. This shows us that price elasticity of demand changes at different points along a straight-line demand curve.

Calculating the Price Elasticity of Supply

Assume that an apartment rents for $650 per month and at that price the landlord rents 10,000 units are rented as Figure 5.3 shows. When the price increases to $700 per month, the landlord supplies 13,000 units into the market. By what percentage does apartment supply increase? What is the price sensitivity?

The graph shows an upward sloping line that represents the supply of apartment rentals.
Figure 5.3 Price Elasticity of Supply We calculate the price elasticity of supply as the percentage change in quantity divided by the percentage change in price.

Using the Midpoint Method,

% change in quantity=13,00010,000(13,000+10,000)/2 × 100=3,00011,500 × 100=26.1% change in price=$700$650($700+$650)/2 × 100=50675 × 100=7.4Price Elasticity of Supply=26.1%  7.4%=3.53% change in quantity=13,00010,000(13,000+10,000)/2 × 100=3,00011,500 × 100=26.1% change in price=$700$650($700+$650)/2 × 100=50675 × 100=7.4Price Elasticity of Supply=26.1%  7.4%=3.53

Again, as with the elasticity of demand, the elasticity of supply is not followed by any units. Elasticity is a ratio of one percentage change to another percentage change—nothing more—and we read it as an absolute value. In this case, a 1% rise in price causes an increase in quantity supplied of 3.5%. The greater than one elasticity of supply means that the percentage change in quantity supplied will be greater than a one percent price change. If you're starting to wonder if the concept of slope fits into this calculation, read the following Clear It Up box.

Clear It Up

Is the elasticity the slope?

It is a common mistake to confuse the slope of either the supply or demand curve with its elasticity. The slope is the rate of change in units along the curve, or the rise/run (change in y over the change in x). For example, in Figure 5.2, at each point shown on the demand curve, price drops by $10 and the number of units demanded increases by 200 compared to the point to its left. The slope is –10/200 along the entire demand curve and does not change. The price elasticity, however, changes along the curve. Elasticity between points A and B was 0.45 and increased to 1.47 between points G and H. Elasticity is the percentage change, which is a different calculation from the slope and has a different meaning.

When we are at the upper end of a demand curve, where price is high and the quantity demanded is low, a small change in the quantity demanded, even in, say, one unit, is pretty big in percentage terms. A change in price of, say, a dollar, is going to be much less important in percentage terms than it would have been at the bottom of the demand curve. Likewise, at the bottom of the demand curve, that one unit change when the quantity demanded is high will be small as a percentage.

Thus, at one end of the demand curve, where we have a large percentage change in quantity demanded over a small percentage change in price, the elasticity value would be high, or demand would be relatively elastic. Even with the same change in the price and the same change in the quantity demanded, at the other end of the demand curve the quantity is much higher, and the price is much lower, so the percentage change in quantity demanded is smaller and the percentage change in price is much higher. That means at the bottom of the curve we'd have a small numerator over a large denominator, so the elasticity measure would be much lower, or inelastic.

As we move along the demand curve, the values for quantity and price go up or down, depending on which way we are moving, so the percentages for, say, a $1 difference in price or a one unit difference in quantity, will change as well, which means the ratios of those percentages and hence the elasticity will change.

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