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Principles of Economics 2e

6.2 How Changes in Income and Prices Affect Consumption Choices

Principles of Economics 2e6.2 How Changes in Income and Prices Affect Consumption Choices
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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 Consumer Choices
    1. Introduction to Consumer Choices
    2. 6.1 Consumption Choices
    3. 6.2 How Changes in Income and Prices Affect Consumption Choices
    4. 6.3 Behavioral Economics: An Alternative Framework for Consumer Choice
    5. Key Terms
    6. Key Concepts and Summary
    7. Self-Check Questions
    8. Review Questions
    9. Critical Thinking Questions
    10. Problems
  8. 7 Production, Costs, and Industry Structure
    1. Introduction to Production, Costs, and Industry Structure
    2. 7.1 Explicit and Implicit Costs, and Accounting and Economic Profit
    3. 7.2 Production in the Short Run
    4. 7.3 Costs in the Short Run
    5. 7.4 Production in the Long Run
    6. 7.5 Costs in the Long Run
    7. Key Terms
    8. Key Concepts and Summary
    9. Self-Check Questions
    10. Review Questions
    11. Critical Thinking Questions
    12. Problems
  9. 8 Perfect Competition
    1. Introduction to Perfect Competition
    2. 8.1 Perfect Competition and Why It Matters
    3. 8.2 How Perfectly Competitive Firms Make Output Decisions
    4. 8.3 Entry and Exit Decisions in the Long Run
    5. 8.4 Efficiency in Perfectly Competitive Markets
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  10. 9 Monopoly
    1. Introduction to a Monopoly
    2. 9.1 How Monopolies Form: Barriers to Entry
    3. 9.2 How a Profit-Maximizing Monopoly Chooses Output and Price
    4. Key Terms
    5. Key Concepts and Summary
    6. Self-Check Questions
    7. Review Questions
    8. Critical Thinking Questions
    9. Problems
  11. 10 Monopolistic Competition and Oligopoly
    1. Introduction to Monopolistic Competition and Oligopoly
    2. 10.1 Monopolistic Competition
    3. 10.2 Oligopoly
    4. Key Terms
    5. Key Concepts and Summary
    6. Self-Check Questions
    7. Review Questions
    8. Critical Thinking Questions
    9. Problems
  12. 11 Monopoly and Antitrust Policy
    1. Introduction to Monopoly and Antitrust Policy
    2. 11.1 Corporate Mergers
    3. 11.2 Regulating Anticompetitive Behavior
    4. 11.3 Regulating Natural Monopolies
    5. 11.4 The Great Deregulation Experiment
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  13. 12 Environmental Protection and Negative Externalities
    1. Introduction to Environmental Protection and Negative Externalities
    2. 12.1 The Economics of Pollution
    3. 12.2 Command-and-Control Regulation
    4. 12.3 Market-Oriented Environmental Tools
    5. 12.4 The Benefits and Costs of U.S. Environmental Laws
    6. 12.5 International Environmental Issues
    7. 12.6 The Tradeoff between Economic Output and Environmental Protection
    8. Key Terms
    9. Key Concepts and Summary
    10. Self-Check Questions
    11. Review Questions
    12. Critical Thinking Questions
    13. Problems
  14. 13 Positive Externalities and Public Goods
    1. Introduction to Positive Externalities and Public Goods
    2. 13.1 Why the Private Sector Underinvests in Innovation
    3. 13.2 How Governments Can Encourage Innovation
    4. 13.3 Public Goods
    5. Key Terms
    6. Key Concepts and Summary
    7. Self-Check Questions
    8. Review Questions
    9. Critical Thinking Questions
    10. Problems
  15. 14 Labor Markets and Income
    1. Introduction to Labor Markets and Income
    2. 14.1 The Theory of Labor Markets
    3. 14.2 Wages and Employment in an Imperfectly Competitive Labor Market
    4. 14.3 Market Power on the Supply Side of Labor Markets: Unions
    5. 14.4 Bilateral Monopoly
    6. 14.5 Employment Discrimination
    7. 14.6 Immigration
    8. Key Terms
    9. Key Concepts and Summary
    10. Self-Check Questions
    11. Review Questions
    12. Critical Thinking Questions
  16. 15 Poverty and Economic Inequality
    1. Introduction to Poverty and Economic Inequality
    2. 15.1 Drawing the Poverty Line
    3. 15.2 The Poverty Trap
    4. 15.3 The Safety Net
    5. 15.4 Income Inequality: Measurement and Causes
    6. 15.5 Government Policies to Reduce Income Inequality
    7. Key Terms
    8. Key Concepts and Summary
    9. Self-Check Questions
    10. Review Questions
    11. Critical Thinking Questions
    12. Problems
  17. 16 Information, Risk, and Insurance
    1. Introduction to Information, Risk, and Insurance
    2. 16.1 The Problem of Imperfect Information and Asymmetric Information
    3. 16.2 Insurance and Imperfect Information
    4. Key Terms
    5. Key Concepts and Summary
    6. Self-Check Questions
    7. Review Questions
    8. Critical Thinking Questions
    9. Problems
  18. 17 Financial Markets
    1. Introduction to Financial Markets
    2. 17.1 How Businesses Raise Financial Capital
    3. 17.2 How Households Supply Financial Capital
    4. 17.3 How to Accumulate Personal Wealth
    5. Key Terms
    6. Key Concepts and Summary
    7. Self-Check Questions
    8. Review Questions
    9. Critical Thinking Questions
    10. Problems
  19. 18 Public Economy
    1. Introduction to Public Economy
    2. 18.1 Voter Participation and Costs of Elections
    3. 18.2 Special Interest Politics
    4. 18.3 Flaws in the Democratic System of Government
    5. Key Terms
    6. Key Concepts and Summary
    7. Self-Check Questions
    8. Review Questions
    9. Critical Thinking Questions
    10. Problems
  20. 19 The Macroeconomic Perspective
    1. Introduction to the Macroeconomic Perspective
    2. 19.1 Measuring the Size of the Economy: Gross Domestic Product
    3. 19.2 Adjusting Nominal Values to Real Values
    4. 19.3 Tracking Real GDP over Time
    5. 19.4 Comparing GDP among Countries
    6. 19.5 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
  21. 20 Economic Growth
    1. Introduction to Economic Growth
    2. 20.1 The Relatively Recent Arrival of Economic Growth
    3. 20.2 Labor Productivity and Economic Growth
    4. 20.3 Components of Economic Growth
    5. 20.4 Economic Convergence
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  22. 21 Unemployment
    1. Introduction to Unemployment
    2. 21.1 How Economists Define and Compute Unemployment Rate
    3. 21.2 Patterns of Unemployment
    4. 21.3 What Causes Changes in Unemployment over the Short Run
    5. 21.4 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
  23. 22 Inflation
    1. Introduction to Inflation
    2. 22.1 Tracking Inflation
    3. 22.2 How to Measure Changes in the Cost of Living
    4. 22.3 How the U.S. and Other Countries Experience Inflation
    5. 22.4 The Confusion Over Inflation
    6. 22.5 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
  24. 23 The International Trade and Capital Flows
    1. Introduction to the International Trade and Capital Flows
    2. 23.1 Measuring Trade Balances
    3. 23.2 Trade Balances in Historical and International Context
    4. 23.3 Trade Balances and Flows of Financial Capital
    5. 23.4 The National Saving and Investment Identity
    6. 23.5 The Pros and Cons of Trade Deficits and Surpluses
    7. 23.6 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
  25. 24 The Aggregate Demand/Aggregate Supply Model
    1. Introduction to the Aggregate Supply–Aggregate Demand Model
    2. 24.1 Macroeconomic Perspectives on Demand and Supply
    3. 24.2 Building a Model of Aggregate Demand and Aggregate Supply
    4. 24.3 Shifts in Aggregate Supply
    5. 24.4 Shifts in Aggregate Demand
    6. 24.5 How the AD/AS Model Incorporates Growth, Unemployment, and Inflation
    7. 24.6 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
  26. 25 The Keynesian Perspective
    1. Introduction to the Keynesian Perspective
    2. 25.1 Aggregate Demand in Keynesian Analysis
    3. 25.2 The Building Blocks of Keynesian Analysis
    4. 25.3 The Phillips Curve
    5. 25.4 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
  27. 26 The Neoclassical Perspective
    1. Introduction to the Neoclassical Perspective
    2. 26.1 The Building Blocks of Neoclassical Analysis
    3. 26.2 The Policy Implications of the Neoclassical Perspective
    4. 26.3 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
  28. 27 Money and Banking
    1. Introduction to Money and Banking
    2. 27.1 Defining Money by Its Functions
    3. 27.2 Measuring Money: Currency, M1, and M2
    4. 27.3 The Role of Banks
    5. 27.4 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
  29. 28 Monetary Policy and Bank Regulation
    1. Introduction to Monetary Policy and Bank Regulation
    2. 28.1 The Federal Reserve Banking System and Central Banks
    3. 28.2 Bank Regulation
    4. 28.3 How a Central Bank Executes Monetary Policy
    5. 28.4 Monetary Policy and Economic Outcomes
    6. 28.5 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
  30. 29 Exchange Rates and International Capital Flows
    1. Introduction to Exchange Rates and International Capital Flows
    2. 29.1 How the Foreign Exchange Market Works
    3. 29.2 Demand and Supply Shifts in Foreign Exchange Markets
    4. 29.3 Macroeconomic Effects of Exchange Rates
    5. 29.4 Exchange Rate Policies
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  31. 30 Government Budgets and Fiscal Policy
    1. Introduction to Government Budgets and Fiscal Policy
    2. 30.1 Government Spending
    3. 30.2 Taxation
    4. 30.3 Federal Deficits and the National Debt
    5. 30.4 Using Fiscal Policy to Fight Recession, Unemployment, and Inflation
    6. 30.5 Automatic Stabilizers
    7. 30.6 Practical Problems with Discretionary Fiscal Policy
    8. 30.7 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
  32. 31 The Impacts of Government Borrowing
    1. Introduction to the Impacts of Government Borrowing
    2. 31.1 How Government Borrowing Affects Investment and the Trade Balance
    3. 31.2 Fiscal Policy and the Trade Balance
    4. 31.3 How Government Borrowing Affects Private Saving
    5. 31.4 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
  33. 32 Macroeconomic Policy Around the World
    1. Introduction to Macroeconomic Policy around the World
    2. 32.1 The Diversity of Countries and Economies across the World
    3. 32.2 Improving Countries’ Standards of Living
    4. 32.3 Causes of Unemployment around the World
    5. 32.4 Causes of Inflation in Various Countries and Regions
    6. 32.5 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
  34. 33 International Trade
    1. Introduction to International Trade
    2. 33.1 Absolute and Comparative Advantage
    3. 33.2 What Happens When a Country Has an Absolute Advantage in All Goods
    4. 33.3 Intra-industry Trade between Similar Economies
    5. 33.4 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
  35. 34 Globalization and Protectionism
    1. Introduction to Globalization and Protectionism
    2. 34.1 Protectionism: An Indirect Subsidy from Consumers to Producers
    3. 34.2 International Trade and Its Effects on Jobs, Wages, and Working Conditions
    4. 34.3 Arguments in Support of Restricting Imports
    5. 34.4 How Governments Enact Trade Policy: Globally, Regionally, and Nationally
    6. 34.5 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
  36. A | The Use of Mathematics in Principles of Economics
  37. B | Indifference Curves
  38. C | Present Discounted Value
  39. D | The Expenditure-Output Model
  40. 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
    22. Chapter 22
    23. Chapter 23
    24. Chapter 24
    25. Chapter 25
    26. Chapter 26
    27. Chapter 27
    28. Chapter 28
    29. Chapter 29
    30. Chapter 30
    31. Chapter 31
    32. Chapter 32
    33. Chapter 33
    34. Chapter 34
  41. References
  42. Index

By the end of this section, you will be able to:

  • Explain how income, prices, and preferences affect consumer choices
  • Contrast the substitution effect and the income effect
  • Utilize concepts of demand to analyze consumer choices
  • Apply utility-maximizing choices to governments and businesses

Just as we can use utility and marginal utility to discuss making consumer choices along a budget constraint, we can also use these ideas to think about how consumer choices change when the budget constraint shifts in response to changes in income or price. Because we can use the budget constraint framework to analyze how quantities demanded change because of price movements, the budget constraint model can illustrate the underlying logic behind demand curves.

How Changes in Income Affect Consumer Choices

Let’s begin with a concrete example illustrating how changes in income level affect consumer choices. Figure 6.3 shows a budget constraint that represents Kimberly’s choice between concert tickets at $50 each and getting away overnight to a bed-and-breakfast for $200 per night. Kimberly has $1,000 per year to spend between these two choices. After thinking about her total utility and marginal utility and applying the decision rule that the ratio of the marginal utilities to the prices should be equal between the two products, Kimberly chooses point M, with eight concerts and three overnight getaways as her utility-maximizing choice.

The graph's various points represent which good is viewed as inferior. The first solid downward sloping line represents the original budget constraint. The second budget constraint represents a different set of options based on the consumer having more money to spend on both items.
Figure 6.3 How a Change in Income Affects Consumption Choices The utility-maximizing choice on the original budget constraint is M. The dashed horizontal and vertical lines extending through point M allow you to see at a glance whether the quantity consumed of goods on the new budget constraint is higher or lower than on the original budget constraint. On the new budget constraint, Kimberly will make a choice like N if both goods are normal goods. If overnight stays is an inferior good, Kimberly will make a choice like P. If concert tickets are an inferior good, Kimberly will make a choice like Q.

Now, assume that the income Kimberly has to spend on these two items rises to $2,000 per year, causing her budget constraint to shift out to the right. How does this rise in income alter her utility-maximizing choice? Kimberly will again consider the utility and marginal utility that she receives from concert tickets and overnight getaways and seek her utility-maximizing choice on the new budget line, but how will her new choice relate to her original choice?

We can replace the possible choices along the new budget constraint into three groups, which the dashed horizontal and vertical lines that pass through the original choice M in the figure divide. All choices on the upper left of the new budget constraint that are to the left of the vertical dashed line, like choice P with two overnight stays and 32 concert tickets, involve less of the good on the horizontal axis but much more of the good on the vertical axis. All choices to the right of the vertical dashed line and above the horizontal dashed line—like choice N with five overnight getaways and 20 concert tickets—have more consumption of both goods. Finally, all choices that are to the right of the vertical dashed line but below the horizontal dashed line, like choice Q with four concerts and nine overnight getaways, involve less of the good on the vertical axis but much more of the good on the horizontal axis.

All of these choices are theoretically possible, depending on Kimberly’s personal preferences as expressed through the total and marginal utility she would receive from consuming these two goods. When income rises, the most common reaction is to purchase more of both goods, like choice N, which is to the upper right relative to Kimberly’s original choice M, although exactly how much more of each good will vary according to personal taste. Conversely, when income falls, the most typical reaction is to purchase less of both goods. As we defined in the chapter on Demand and Supply and again in the chapter on Elasticity, we call goods and services normal goods when a rise in income leads to a rise in the quantity consumed of that good and a fall in income leads to a fall in quantity consumed.

However, depending on Kimberly’s preferences, a rise in income could cause consumption of one good to increase while consumption of the other good declines. A choice like P means that a rise in income caused her quantity consumed of overnight stays to decline, while a choice like Q would mean that a rise in income caused her quantity of concerts to decline. Goods where demand declines as income rises (or conversely, where the demand rises as income falls) are called “inferior goods.” An inferior good occurs when people trim back on a good as income rises, because they can now afford the more expensive choices that they prefer. For example, a higher-income household might eat fewer hamburgers or be less likely to buy a used car, and instead eat more steak and buy a new car.

How Price Changes Affect Consumer Choices

For analyzing the possible effect of a change in price on consumption, let’s again use a concrete example. Figure 6.4 represents Sergei's consumer choice, who chooses between purchasing baseball bats and cameras. A price increase for baseball bats would have no effect on the ability to purchase cameras, but it would reduce the number of bats Sergei could afford to buy. Thus a price increase for baseball bats, the good on the horizontal axis, causes the budget constraint to rotate inward, as if on a hinge, from the vertical axis. As in the previous section, the point labeled M represents the originally preferred point on the original budget constraint, which Sergei has chosen after contemplating his total utility and marginal utility and the tradeoffs involved along the budget constraint. In this example, the units along the horizontal and vertical axes are not numbered, so the discussion must focus on whether Sergei will consume more or less of certain goods, not on numerical amounts.

The graph shows how price changes influence spending choices.
Figure 6.4 How a Change in Price Affects Consumption Choices The original utility-maximizing choice is M. When the price rises, the budget constraint rotates clockwise. The dashed lines make it possible to see at a glance whether the new consumption choice involves less of both goods, or less of one good and more of the other. The new possible choices would be fewer baseball bats and more cameras, like point H, or less of both goods, as at point J. Choice K would mean that the higher price of bats led to exactly the same quantity of bat consumption, but fewer cameras. Theoretically possible, but unlikely in the real world, we rule out choices like L because they would mean that a higher price for baseball bats means a greater consumption of baseball bats.

After the price increase, Sergei will make a choice along the new budget constraint. Again, we can divide his choices into three segments by the dashed vertical and horizontal lines. In the upper left portion of the new budget constraint, at a choice like H, Sergei consumes more cameras and fewer bats. In the central portion of the new budget constraint, at a choice like J, he consumes less of both goods. At the right-hand end, at a choice like L, he consumes more bats but fewer cameras.

The typical response to higher prices is that a person chooses to consume less of the product with the higher price. This occurs for two reasons, and both effects can occur simultaneously. The substitution effect occurs when a price changes and consumers have an incentive to consume less of the good with a relatively higher price and more of the good with a relatively lower price. The income effect is that a higher price means, in effect, the buying power of income has been reduced (even though actual income has not changed), which leads to buying less of the good (when the good is normal). In this example, the higher price for baseball bats would cause Sergei to buy fewer bats for both reasons. Exactly how much will a higher price for bats cause Sergei's bat consumption to fall? Figure 6.4 suggests a range of possibilities. Sergei might react to a higher price for baseball bats by purchasing the same quantity of bats, but cutting his camera consumption. This choice is the point K on the new budget constraint, straight below the original choice M. Alternatively, Sergei might react by dramatically reducing his bat purchases and instead buy more cameras.

The key is that it would be imprudent to assume that a change in baseball bats will only or primarily affect the good's price whose price is changed, while the quantity consumed of other goods remains the same. Since Sergei purchases all his products out of the same budget, a change in the price of one good can also have a range of effects, either positive or negative, on the quantity consumed of other goods.

In short, a higher price typically causes reduced consumption of the good in question, but it can affect the consumption of other goods as well.

Link It Up

Read this article about the potential of variable prices in vending machines.

The Foundations of Demand Curves

Changes in the price of a good lead the budget constraint to rotate. A rotation in the budget constraint means that when individuals are seeking their highest utility, the quantity that is demanded of that good will change. In this way, the logical foundations of demand curves—which show a connection between prices and quantity demanded—are based on the underlying idea of individuals seeking utility. Figure 6.5 (a) shows a budget constraint with a choice between housing and “everything else.” (Putting “everything else” on the vertical axis can be a useful approach in some cases, especially when the focus of the analysis is on one particular good.) We label the preferred choice on the original budget constraint that provides the highest possible utility M0. The other three budget constraints represent successively higher prices for housing of P1, P2, and P3. As the budget constraint rotates in, and in, and in again, we label the utility-maximizing choices M1, M2, and M3, and the quantity demanded of housing falls from Q0 to Q1 to Q2 to Q3.

The two graphs show how budget constraints influence the demand curve.
Figure 6.5 The Foundations of a Demand Curve: An Example of Housing (a) As the price increases from P0 to P1 to P2 to P3, the budget constraint on the upper part of the diagram rotates clockwise. The utility-maximizing choice changes from M0 to M1 to M2 to M3. As a result, the quantity demanded of housing shifts from Q0 to Q1 to Q2 to Q3, ceteris paribus. (b) The demand curve graphs each combination of the price of housing and the quantity of housing demanded, ceteris paribus. The quantities of housing are the same at the points on both (a) and (b). Thus, the original price of housing (P0) and the original quantity of housing (Q0) appear on the demand curve as point E0. The higher price of housing (P1) and the corresponding lower quantity demanded of housing (Q1) appear on the demand curve as point E1.

Thus, as the price of housing rises, the budget constraint rotates clockwise and the quantity consumed of housing falls, ceteris paribus (meaning, with all other things being the same). We graph this relationship—the price of housing rising from P0 to P1 to P2 to P3, while the quantity of housing demanded falls from Q0 to Q1 to Q2 to Q3—on the demand curve in Figure 6.5 (b). The vertical dashed lines stretching between the top and bottom of Figure 6.5 show that the quantity of housing demanded at each point is the same in both (a) and (b). We ultimately determine the shape of a demand curve by the underlying choices about maximizing utility subject to a budget constraint. While economists may not be able to measure “utils,” they can certainly measure price and quantity demanded.

Applications in Government and Business

The budget constraint framework for making utility-maximizing choices offers a reminder that people can react to a change in price or income in a range of different ways. For example, in the winter months of 2005, costs for heating homes increased significantly in many parts of the country as prices for natural gas and electricity soared, due in large part to the disruption caused by Hurricanes Katrina and Rita. Some people reacted by reducing the quantity demanded of energy; for example, by turning down the thermostats in their homes by a few degrees and wearing a heavier sweater inside. Even so, many home heating bills rose, so people adjusted their consumption in other ways, too. As you learned in the chapter on Elasticity, the short run demand for home heating is generally inelastic. Each household cut back on what it valued least on the margin. For some it might have been some dinners out, or a vacation, or postponing buying a new refrigerator or a new car. Sharply higher energy prices can have effects beyond the energy market, leading to a widespread reduction in purchasing throughout the rest of the economy.

A similar issue arises when the government imposes taxes on certain products, such as on gasoline, cigarettes, and alcohol. Say that a tax on alcohol leads to a higher price at the liquor store. The higher price of alcohol causes the budget constraint to pivot left, and alcoholic beverage consumption is likely to decrease. However, people may also react to the higher price of alcoholic beverages by cutting back on other purchases. For example, they might cut back on snacks at restaurants like chicken wings and nachos. It would be unwise to assume that the liquor industry is the only one affected by the tax on alcoholic beverages. Read the next Clear It Up to learn about how who controls the household income influences buying decisions.

The Unifying Power of the Utility-Maximizing Budget Set Framework

An interaction between prices, budget constraints, and personal preferences determine household choices. The flexible and powerful terminology of utility-maximizing gives economists a vocabulary for bringing these elements together.

Not even economists believe that people walk around mumbling about their marginal utilities before they walk into a shopping mall, accept a job, or make a deposit in a savings account. However, economists do believe that individuals seek their own satisfaction or utility and that people often decide to try a little less of one thing and a little more of another. If we accept these assumptions, then the idea of utility-maximizing households facing budget constraints becomes highly plausible.

Clear It Up

Does who controls household income make a difference?

In the mid-1970s, the United Kingdom made an interesting policy change in its “child allowance” policy. This program provides a fixed amount of money per child to every family, regardless of family income. Traditionally, the child allowance had been distributed to families by withholding less in taxes from the paycheck of the family wage earner—typically the father in this time period. The new policy instead provided the child allowance as a cash payment to the mother. As a result of this change, households have the same level of income and face the same prices in the market, but the money is more likely to be in the mother's purse than in the father's wallet.

Should this change in policy alter household consumption patterns? Basic models of consumption decisions, of the sort that we examined in this chapter, assume that it does not matter whether the mother or the father receives the money, because both parents seek to maximize the family's utility as a whole. In effect, this model assumes that everyone in the family has the same preferences.

In reality, the share of that the father or mother controls does affect what the household consumes. When the mother controls a larger share of family income a number of studies, in the United Kingdom and in a wide variety of other countries, have found that the family tends to spend more on restaurant meals, child care, and women’s clothing, and less on alcohol and tobacco. As the mother controls a larger share of household resources, children’s health improves, too. These findings suggest that when providing assistance to poor families, in high-income countries and low-income countries alike, the monetary amount of assistance is not all that matters: it also matters which family member actually receives the money.

The budget constraint framework serves as a constant reminder to think about the full range of effects that can arise from changes in income or price, not just effects on the one product that might seem most immediately affected.

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