August 21, 2017 

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LAGGING ECONOMIC INDICATOR: One of seven economic statistics that tend to move up or down a few months after the expansions and contractions of the business cycle. These statistics paint a pretty clear picture of what the economy was doing a few months back. Lagging economic indicators lag the turning points of the aggregate economy by 3-12 months. After a contraction begins, lagging indicators decline 3 to 12 months later. And 3 to 12 months after a expansion begins, lagging indicators rise.

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A macroeconomic model that balances non-consumption expenditures on production (injections) and non-consumption uses of income (leakages) that is used to identify the equilibrium level of, and analyze disruptions to, aggregate production and income. The injections-leakages model is based on the principles of Keynesian economics and provides an alternative to the standard aggregate expenditures (Keynesian cross) analysis. The three injections included in the model are investment expenditures, government purchases, and exports. The three leakages included in the model are saving, taxes, and imports. Three variations are the two-sector injections-leakages model (or saving-investment model), three-sector injections-leakages model, and four-sector injections-leakages model.
The injections-leakages model provides an alternative to the more common Keynesian cross, aggregate expenditures-aggregate production model of the macroeconomy. Both models provide essentially the same analysis and are essentially "two sides of the same coin." The key difference between the two models is that consumption is explicitly eliminated from the injections-leakages variation. Whereas the Keynesian cross builds on the consumption function, the injections-leakages model builds on the saving function',500,400)">saving function.

A Keynesian Overview

Keynesian economics is a theory of macroeconomics developed by John Maynard Keynes based on the proposition that aggregate demand is the primary source of business-cycle instability and the most important cause of recessions. Keynesian economics points to discretionary government policies, especially fiscal policy, as the primary means of stabilizing business cycles and tends to be favored by those on the liberal end of the political spectrum.

The basic principles of Keynesian economics were developed by Keynes in his book, The General Theory of Employment, Interest and Money, published in 1936. This work launched the modern study of macroeconomics and served as a guide for both macroeconomic theory and macroeconomic policies for four decades.

Injections and Leakages

One half of the injections-leakages model is injections, which are non-consumption expenditures on aggregate production. The three injections are investment expenditures, government purchases, and exports. These are termed injections because they are "injected" into the core circular flow of consumption, production, and income.

The other half of the injections-leakages model is leakages, which are non-consumption uses of the income generated from production. The three leakages are saving, taxes, and imports. These are termed leakages because they are "leaked" out of the core circular flow of consumption, production, and income.

Equilibrium in the injections-leakages model relies on a balance between the injections into the core circular flow and leakages out of the flow. If leakages match injections, then the volume of the core circular flow does not change. This is the same as achieving a balance between the water flowing form a faucet into a sink and that flowing out through the drain. When these two flows are equal, then the total amount of water IN the sink does not change. Equilibrium!

The Circular Flow

The Circular Flow
The Circular Flow

Injections and leakages can be best illustrated using the standard circular flow model of the macroeconomy, such as that presented in the exhibit to the right. The circular flow is a handy model of macroeconomic activity that highlights the interaction between households and businesses through the product and resource markets.

The business sector is at the right and the household sector is at the left. The product markets are at the top and the resource markets are at the bottom. The household sector buys production from the business sector through the product markets. Expenditures by the household sector are consumption expenditures. Revenue going to the business sector is gross domestic product.

The business sector hires factor services from the household sector through the resource markets. Payments made by the business sector are factor payments. Income going to the household sector is national income.

These four parts -- consumption expenditures, gross domestic product, factor payments, and national income -- are the core of the circular flow. They are the "engine" that drives the macroeconomy.

Let's now consider how injections and leakages relate to this core circular flow.

  • Injections: The three injections -- investment, government purchases, and exports -- can be displayed by clicking the [Injections] button. These injection expenditures, like consumption, are used to purchase aggregate production through the product markets. Most importantly, injections add to the total volume of the basic circular flow. That is, they "inject" revenue into the product markets that is used for factor payments and becomes household income.

  • Leakages: The three leakages -- saving, taxes, and imports -- can be displayed by clicking the [Leakages"] button. These leakages, like consumption, are how the household sector divides up or uses its income. Most importantly, leakages subtract from the total volume of the basic circular flow. That is, they "leak" income away from the product markets, making less available for factor payments and household income.
The critical implication from the circular flow is that a balance between injections and leakages maintains a constant flow of income, consumption, production, and factor payments moving between the household and business sectors. This is the essence of macroeconomic equilibrium -- the level of aggregate production remains unchanged.

However, if injections exceed leakages, then the volume of the basic flow expands and aggregate production increases. Alternatively, if leakages exceed injections, then the volume of the basic flow contracts and aggregate production decreases. As we shall see, this change in production is what moves the economy to an equilibrium balance.

The Injections-Leakages Balance

A balance between injections and leakages generates the same equilibrium as a balance between aggregate expenditures and aggregate production. A little manipulation of the Y = AE equilibrium condition illustrates why.
  • Aggregate expenditures (AE) are the sum of consumption (C), investment (I), government purchases (G), and net exports (X - M).

    AE = C + I + G + (X - M)

  • The income generated by aggregate production (Y) is used by the household sector for consumption (C), saving (S), and taxes (T).

    Y = C + S + T

  • Substituting each of these equations into the Y = AE equilibrium condition gives us:

    C + S + T = C + I + G + (X - M)

  • Because consumption (C) is on both sides, it cancels out.

    S + T = I + G + (X - M)

  • For reasons that will be apparent later, let's move imports (M) to the left-hand side.

    S + T + M = I + G + X

This last equation indicates that equilibrium can be achieved by equating injections I + G + X with leakages S + T + M. Most importantly, when aggregate expenditures equal aggregate production (Y = AE), then injections are necessarily equal to leakages S + T + M = I + G + X.

The Graphical Model

The Injections-Leakages Model
The exhibit to the right presents the injections-leakages model. The horizontal green line, labeled I + G + X, is the injections line and includes investment expenditures (I), government purchases (G), and exports (X). The positively-sloped red line, labeled S + T + M, is the leakages line and includes saving (S), taxes (T), and imports (M). The intersection of the two lines is the equilibrium level of aggregate production, which matches the equilibrium level of aggregate production generated by the Keynesian cross version of the Keynesian model.

Three Variations

The injections-leakages model comes in three common variations, each based on a different combination of the four macroeconomic sectors, and thus a different number of injections and leakages.
  • Two-Sector Model: The simplest injections-leakages model includes the household and business sectors. Also termed the saving-investment model, this variation is often used to illustrate the basic operation of the model, including adjustment to equilibrium and the multiplier process. The two-sector model captures the role of induced activity through household saving and the role of autonomous expenditures through business investment. Saving is the only leakage and investment is the only injection.

  • Three-Sector Model: The second variation of the injections-leakages model adds the government (or public) sector to the household and business sectors contained in the two-sector model. This variation is used to analyze government stabilization policies, especially how fiscal policy changes in government purchases and taxes can be used to close recessionary gaps and inflationary gaps. Saving and taxes are the two leakages. Investment and government purchases are the two injections.

  • Four-Sector Model: As the name suggests, all four macroeconomic sectors--household, business, government, and foreign--are included in the four-sector Keynesian model. This model is not only used to capture the interaction between the domestic economic and the foreign sector, but also provides the foundation for detailed, empirically estimated models of the macroeconomy. Saving, taxes, and imports are the three leakages. Investment, government purchases, and exports are the three injections.


Recommended Citation:

INJECTIONS-LEAKAGES MODEL, AmosWEB Encyclonomic WEB*pedia,, AmosWEB LLC, 2000-2017. [Accessed: August 21, 2017].

Check Out These Related Terms...

     | injections | leakages | injections line | leakages line | saving-investment model | two-sector injections-leakages model | three-sector injections-leakages model | four-sector injections-leakages model | Keynesian model |

Or For A Little Background...

     | Keynesian economics | Keynesian cross | aggregate expenditures | saving line | investment line | effective demand | induced expenditures | autonomous expenditures | macroeconomics | macroeconomic sectors | saving | investment expenditures | government purchases | taxes | imports | exports |

And For Further Study...

     | expansionary fiscal policy | contractionary fiscal policy | automatic stabilizers | Keynesian cross and aggregate market | expenditures multiplier | accelerator principle | paradox of thrift | aggregate market analysis | business cycles |

Related Websites (Will Open in New Window)...

     | The General Theory of Employment, Interest, and Money |

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