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Principles of Macroeconomics for AP® Courses

10.2 Building a Model of Aggregate Demand and Aggregate Supply

Principles of Macroeconomics for AP® Courses10.2 Building a Model of Aggregate Demand and Aggregate Supply
  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 Economies Can Be Organized: 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 The Macroeconomic Perspective
    1. Introduction to the Macroeconomic Perspective
    2. 5.1 Measuring the Size of the Economy: Gross Domestic Product
    3. 5.2 Adjusting Nominal Values to Real Values
    4. 5.3 Tracking Real GDP over Time
    5. 5.4 Comparing GDP among Countries
    6. 5.5 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
  7. 6 Economic Growth
    1. Introduction to Economic Growth
    2. 6.1 The Relatively Recent Arrival of Economic Growth
    3. 6.2 Labor Productivity and Economic Growth
    4. 6.3 Components of Economic Growth
    5. 6.4 Economic Convergence
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  8. 7 Unemployment
    1. Introduction to Unemployment
    2. 7.1 How the Unemployment Rate Is Defined and Computed
    3. 7.2 Patterns of Unemployment
    4. 7.3 What Causes Changes in Unemployment over the Short Run
    5. 7.4 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
  9. 8 Inflation
    1. Introduction to Inflation
    2. 8.1 Tracking Inflation
    3. 8.2 How Changes in the Cost of Living Are Measured
    4. 8.3 How the U.S. and Other Countries Experience Inflation
    5. 8.4 The Confusion Over Inflation
    6. 8.5 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
  10. 9 The International Trade and Capital Flows
    1. Introduction to the International Trade and Capital Flows
    2. 9.1 Measuring Trade Balances
    3. 9.2 Trade Balances in Historical and International Context
    4. 9.3 Trade Balances and Flows of Financial Capital
    5. 9.4 The National Saving and Investment Identity
    6. 9.5 The Pros and Cons of Trade Deficits and Surpluses
    7. 9.6 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
  11. 10 The Aggregate Demand/Aggregate Supply Model
    1. Introduction to the Aggregate Demand/Aggregate Supply Model
    2. 10.1 Macroeconomic Perspectives on Demand and Supply
    3. 10.2 Building a Model of Aggregate Demand and Aggregate Supply
    4. 10.3 Shifts in Aggregate Supply
    5. 10.4 Shifts in Aggregate Demand
    6. 10.5 How the AD/AS Model Incorporates Growth, Unemployment, and Inflation
    7. 10.6 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
  12. 11 The Keynesian Perspective
    1. Introduction to the Keynesian Perspective
    2. 11.1 Aggregate Demand in Keynesian Analysis
    3. 11.2 The Building Blocks of Keynesian Analysis
    4. 11.3 The Expenditure-Output (or Keynesian Cross) Model
    5. 11.4 The Phillips Curve
    6. 11.5 The Keynesian Perspective on Market Forces
    7. Key Terms
    8. Key Concepts and Summary
    9. Self-Check Questions
    10. Review Questions
    11. Critical Thinking Questions
  13. 12 The Neoclassical Perspective
    1. Introduction to the Neoclassical Perspective
    2. 12.1 The Building Blocks of Neoclassical Analysis
    3. 12.2 The Policy Implications of the Neoclassical Perspective
    4. 12.3 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
  14. 13 Money and Banking
    1. Introduction to Money and Banking
    2. 13.1 Defining Money by Its Functions
    3. 13.2 Measuring Money: Currency, M1, and M2
    4. 13.3 The Role of Banks
    5. 13.4 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
  15. 14 Monetary Policy and Bank Regulation
    1. Introduction to Monetary Policy and Bank Regulation
    2. 14.1 The Federal Reserve Banking System and Central Banks
    3. 14.2 Bank Regulation
    4. 14.3 How a Central Bank Executes Monetary Policy
    5. 14.4 Monetary Policy and Economic Outcomes
    6. 14.5 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
  16. 15 Exchange Rates and International Capital Flows
    1. Introduction to Exchange Rates and International Capital Flows
    2. 15.1 How the Foreign Exchange Market Works
    3. 15.2 Demand and Supply Shifts in Foreign Exchange Markets
    4. 15.3 Macroeconomic Effects of Exchange Rates
    5. 15.4 Exchange Rate Policies
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  17. 16 Government Budgets and Fiscal Policy
    1. Introduction to Government Budgets and Fiscal Policy
    2. 16.1 Government Spending
    3. 16.2 Taxation
    4. 16.3 Federal Deficits and the National Debt
    5. 16.4 Using Fiscal Policy to Fight Recession, Unemployment, and Inflation
    6. 16.5 Automatic Stabilizers
    7. 16.6 Practical Problems with Discretionary Fiscal Policy
    8. 16.7 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
  18. 17 The Impacts of Government Borrowing
    1. Introduction to the Impacts of Government Borrowing
    2. 17.1 How Government Borrowing Affects Investment and the Trade Balance
    3. 17.2 Fiscal Policy, Investment, and Economic Growth
    4. 17.3 How Government Borrowing Affects Private Saving
    5. 17.4 Fiscal Policy and the Trade Balance
    6. Key Terms
    7. Key Concepts and Summary
    8. Self-Check Questions
    9. Review Questions
    10. Critical Thinking Questions
    11. Problems
  19. 18 Macroeconomic Policy Around the World
    1. Introduction to Macroeconomic Policy around the World
    2. 18.1 The Diversity of Countries and Economies across the World
    3. 18.2 Improving Countries’ Standards of Living
    4. 18.3 Causes of Unemployment around the World
    5. 18.4 Causes of Inflation in Various Countries and Regions
    6. 18.5 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
  20. A | The Use of Mathematics in Principles of Economics
  21. B | Indifference Curves
  22. C | Present Discounted Value
  23. 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
  24. References
  25. Index
By the end of this section, you will be able to:
  • Explain the aggregate supply curve and how it relates to real GDP and potential GDP
  • Explain the aggregate demand curve and how it is influenced by price levels
  • Interpret the aggregate demand/aggregate supply model
  • Identify the point of equilibrium in the aggregate demand/aggregate supply model
  • Define short run aggregate supply and long run aggregate supply

To build a useful macroeconomic model, we need a model that shows what determines total supply or total demand for the economy, and how total demand and total supply interact at the macroeconomic level. This model is called the aggregate demand/aggregate supply model. This module will explain aggregate supply, aggregate demand, and the equilibrium between them. The following modules will discuss the causes of shifts in aggregate supply and aggregate demand.

The Aggregate Supply Curve and Potential GDP

Firms make decisions about what quantity to supply based on the profits they expect to earn. Profits, in turn, are also determined by the price of the outputs the firm sells and by the price of the inputs, like labor or raw materials, the firm needs to buy. Aggregate supply (AS) refers to the total quantity of output (i.e. real GDP) firms will produce and sell. The aggregate supply (AS) curve shows the total quantity of output (i.e. real GDP) that firms will produce and sell at each price level.

Figure 10.3 shows an aggregate supply curve. In the following paragraphs, we will walk through the elements of the diagram one at a time: the horizontal and vertical axes, the aggregate supply curve itself, and the meaning of the potential GDP vertical line.

The graph shows an upward sloping aggregate supply curve. The slope is gradual between 6,500 and 9,000 before become steeper, especially between 9,500 and 9,900.
Figure 10.3 The Aggregate Supply Curve Aggregate supply (AS) slopes up, because as the price level for outputs rises, with the price of inputs remaining fixed, firms have an incentive to produce more and to earn higher profits. The potential GDP line shows the maximum that the economy can produce with full employment of workers and physical capital.

The horizontal axis of the diagram shows real GDP—that is, the level of GDP adjusted for inflation. The vertical axis shows the price level. Remember that the price level is different from the inflation rate. Visualize the price level as an index number, like the GDP deflator, while the inflation rate is the percentage change between price levels over time.

As the price level (the average price of all goods and services produced in the economy) rises, the aggregate quantity of goods and services supplied rises as well. Why? The price level shown on the vertical axis represents prices for final goods or outputs bought in the economy—like the GDP deflator—not the price level for intermediate goods and services that are inputs to production. Thus, the AS curve describes how suppliers will react to a higher price level for final outputs of goods and services, while holding the prices of inputs like labor and energy constant. If firms across the economy face a situation where the price level of what they produce and sell is rising, but their costs of production are not rising, then the lure of higher profits will induce them to expand production.

The slope of an AS curve changes from nearly flat at its far left to nearly vertical at its far right. At the far left of the aggregate supply curve, the level of output in the economy is far below potential GDP, which is defined as the quantity that an economy can produce by fully employing its existing levels of labor, physical capital, and technology, in the context of its existing market and legal institutions. At these relatively low levels of output, levels of unemployment are high, and many factories are running only part-time, or have closed their doors. In this situation, a relatively small increase in the prices of the outputs that businesses sell—while making the assumption of no rise in input prices—can encourage a considerable surge in the quantity of aggregate supply because so many workers and factories are ready to swing into production.

As the quantity produced increases, however, certain firms and industries will start running into limits: perhaps nearly all of the expert workers in a certain industry will have jobs or factories in certain geographic areas or industries will be running at full speed. In the intermediate area of the AS curve, a higher price level for outputs continues to encourage a greater quantity of output—but as the increasingly steep upward slope of the aggregate supply curve shows, the increase in quantity in response to a given rise in the price level will not be quite as large. (Read the following Clear It Up feature to learn why the AS curve crosses potential GDP.)

Clear It Up

Why does AS cross potential GDP?

The aggregate supply curve is typically drawn to cross the potential GDP line. This shape may seem puzzling: How can an economy produce at an output level which is higher than its “potential” or “full employment” GDP? The economic intuition here is that if prices for outputs were high enough, producers would make fanatical efforts to produce: all workers would be on double-overtime, all machines would run 24 hours a day, seven days a week. Such hyper-intense production would go beyond using potential labor and physical capital resources fully, to using them in a way that is not sustainable in the long term. Thus, it is indeed possible for production to sprint above potential GDP, but only in the short run.

At the far right, the aggregate supply curve becomes nearly vertical. At this quantity, higher prices for outputs cannot encourage additional output, because even if firms want to expand output, the inputs of labor and machinery in the economy are fully employed. In this example, the vertical line in the exhibit shows that potential GDP occurs at a total output of 9,500. When an economy is operating at its potential GDP, machines and factories are running at capacity, and the unemployment rate is relatively low—at the natural rate of unemployment. For this reason, potential GDP is sometimes also called full-employment GDP.

The Aggregate Demand Curve

Aggregate demand (AD) refers to the amount of total spending on domestic goods and services in an economy. (Strictly speaking, AD is what economists call total planned expenditure. This distinction will be further explained in the appendix The Expenditure-Output Model. For now, just think of aggregate demand as total spending.) It includes all four components of demand: consumption, investment, government spending, and net exports (exports minus imports). This demand is determined by a number of factors, but one of them is the price level—recall though, that the price level is an index number such as the GDP deflator that measures the average price of the things we buy. The aggregate demand (AD) curve shows the total spending on domestic goods and services at each price level.

Figure 10.4 presents an aggregate demand (AD) curve. Just like the aggregate supply curve, the horizontal axis shows real GDP and the vertical axis shows the price level. The AD curve slopes down, which means that increases in the price level of outputs lead to a lower quantity of total spending. The reasons behind this shape are related to how changes in the price level affect the different components of aggregate demand. The following components make up aggregate demand: consumption spending (C), investment spending (I), government spending (G), and spending on exports (X) minus imports (M): C + I + G + X – M.

The graph shows a downward sloping aggregate demand curve.
Figure 10.4 The Aggregate Demand Curve Aggregate demand (AD) slopes down, showing that, as the price level rises, the amount of total spending on domestic goods and services declines.

The wealth effect holds that as the price level increases, the buying power of savings that people have stored up in bank accounts and other assets will diminish, eaten away to some extent by inflation. Because a rise in the price level reduces people’s wealth, consumption spending will fall as the price level rises.

The interest rate effect is that as prices for outputs rise, the same purchases will take more money or credit to accomplish. This additional demand for money and credit will push interest rates higher. In turn, higher interest rates will reduce borrowing by businesses for investment purposes and reduce borrowing by households for homes and cars—thus reducing consumption and investment spending.

The foreign price effect points out that if prices rise in the United States while remaining fixed in other countries, then goods in the United States will be relatively more expensive compared to goods in the rest of the world. U.S. exports will be relatively more expensive, and the quantity of exports sold will fall. U.S. imports from abroad will be relatively cheaper, so the quantity of imports will rise. Thus, a higher domestic price level, relative to price levels in other countries, will reduce net export expenditures.

Truth be told, among economists all three of these effects are controversial, in part because they do not seem to be very large. For this reason, the aggregate demand curve in Figure 10.4 slopes downward fairly steeply; the steep slope indicates that a higher price level for final outputs reduces aggregate demand for all three of these reasons, but that the change in the quantity of aggregate demand as a result of changes in price level is not very large.

Read the following Work It Out feature to learn how to interpret the AD/AS model. In this example, aggregate supply, aggregate demand, and the price level are given for the imaginary country of Xurbia.

Work It Out

Interpreting the AD/AS Model

Table 10.1 shows information on aggregate supply, aggregate demand, and the price level for the imaginary country of Xurbia. What information does Table 10.1 tell you about the state of the Xurbia’s economy? Where is the equilibrium price level and output level (this is the SR macroequilibrium)? Is Xurbia risking inflationary pressures or facing high unemployment? How can you tell?

Price Level Aggregate Demand Aggregate Supply
110 $700 $600
120 $690 $640
130 $680 $680
140 $670 $720
150 $660 $740
160 $650 $760
170 $640 $770
Table 10.1 Price Level: Aggregate Demand/Aggregate Supply

To begin to use the AD/AS model, it is important to plot the AS and AD curves from the data provided. What is the equilibrium?

Step 1. Draw your x- and y-axis. Label the x-axis Real GDP and the y-axis Price Level.

Step 2. Plot AD on your graph.

Step 3. Plot AS on your graph.

Step 4. Look at Figure 10.5 which provides a visual to aid in your analysis.

The figure shows a downward sloping aggregate demand line intersecting with an aggregate supply curve at approximately (680, 130).
Figure 10.5 The AD/AS Curves AD and AS curves created from the data in Table 10.1.

Step 5. Determine where AD and AS intersect. This is the equilibrium with price level at 130 and real GDP at $680.

Step 6. Look at the graph to determine where equilibrium is located. We can see that this equilibrium is fairly far from where the AS curve becomes near-vertical (or at least quite steep) which seems to start at about $750 of real output. This implies that the economy is not close to potential GDP. Thus, unemployment will be high. In the relatively flat part of the AS curve, where the equilibrium occurs, changes in the price level will not be a major concern, since such changes are likely to be small.

Step 7. Determine what the steep portion of the AS curve indicates. Where the AS curve is steep, the economy is at or close to potential GDP.

Step 8. Draw conclusions from the given information:

  • If equilibrium occurs in the flat range of AS, then economy is not close to potential GDP and will be experiencing unemployment, but stable price level.
  • If equilibrium occurs in the steep range of AS, then the economy is close or at potential GDP and will be experiencing rising price levels or inflationary pressures, but will have a low unemployment rate.

Equilibrium in the Aggregate Demand/Aggregate Supply Model

The intersection of the aggregate supply and aggregate demand curves shows the equilibrium level of real GDP and the equilibrium price level in the economy. At a relatively low price level for output, firms have little incentive to produce, although consumers would be willing to purchase a high quantity. As the price level for outputs rises, aggregate supply rises and aggregate demand falls until the equilibrium point is reached.

Figure 10.6 combines the AS curve from Figure 10.3 and the AD curve from Figure 10.4 and places them both on a single diagram. In this example, the equilibrium point occurs at point E, at a price level of 90 and an output level of 8,800.

The graph shows a downward sloping aggregate demand curve that intersects with an upward sloping aggregate supply curve at the point (8,800, 90).
Figure 10.6 Aggregate Supply and Aggregate Demand The equilibrium, where aggregate supply (AS) equals aggregate demand (AD), occurs at a price level of 90 and an output level of 8,800.

Confusion sometimes arises between the aggregate supply and aggregate demand model and the microeconomic analysis of demand and supply in particular markets for goods, services, labor, and capital. Read the following Clear It Up feature to gain an understanding of whether AS and AD are macro or micro.

Clear It Up

Are AS and AD macro or micro?

These aggregate supply and aggregate demand model and the microeconomic analysis of demand and supply in particular markets for goods, services, labor, and capital have a superficial resemblance, but they also have many underlying differences.

For example, the vertical and horizontal axes have distinctly different meanings in macroeconomic and microeconomic diagrams. The vertical axis of a microeconomic demand and supply diagram expresses a price (or wage or rate of return) for an individual good or service. This price is implicitly relative: it is intended to be compared with the prices of other products (for example, the price of pizza relative to the price of fried chicken). In contrast, the vertical axis of an aggregate supply and aggregate demand diagram expresses the level of a price index like the Consumer Price Index or the GDP deflator—combining a wide array of prices from across the economy. The price level is absolute: it is not intended to be compared to any other prices since it is essentially the average price of all products in an economy. The horizontal axis of a microeconomic supply and demand curve measures the quantity of a particular good or service. In contrast, the horizontal axis of the aggregate demand and aggregate supply diagram measures GDP, which is the sum of all the final goods and services produced in the economy, not the quantity in a specific market.

In addition, the economic reasons for the shapes of the curves in the macroeconomic model are different from the reasons behind the shapes of the curves in microeconomic models. Demand curves for individual goods or services slope down primarily because of the existence of substitute goods, not the wealth effects, interest rate, and foreign price effects associated with aggregate demand curves. The slopes of individual supply and demand curves can have a variety of different slopes, depending on the extent to which quantity demanded and quantity supplied react to price in that specific market, but the slopes of the AS and AD curves are much the same in every diagram (although as we shall see in later chapters, short-run and long-run perspectives will emphasize different parts of the AS curve).

In short, just because the AD/AS diagram has two lines that cross, do not assume that it is the same as every other diagram where two lines cross. The intuitions and meanings of the macro and micro diagrams are only distant cousins from different branches of the economics family tree.

Defining SRAS and LRAS

In the Clear It Up feature titled “Why does AS cross potential GDP?” we differentiated between short run changes in aggregate supply which are shown by the AS curve and long run changes in aggregate supply which are defined by the vertical line at potential GDP. In the short run, if demand is too low (or too high), it is possible for producers to supply less GDP (or more GDP) than potential. In the long run, however, producers are limited to producing at potential GDP. For this reason, what we have been calling the AS curve, will from this point on may also be referred to as the short run aggregate supply (SRAS) curve. The vertical line at potential GDP may also be referred to as the long run aggregate supply (LRAS) curve.

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