Macroéconomie S2 partie 17 " l'équilibre macroéconomique : économie fermée sans secteur public "

Introduction

This tutorial provides a comprehensive overview of macroeconomic equilibrium in a closed economy without a public sector, based on the principles of Keynesian economics. It will guide you through the concepts of equilibrium, investment multipliers, and their implications in a simplified economic model.

Step 1: Understand Macroeconomic Equilibrium

• Definition: Macroeconomic equilibrium occurs when total output (GDP) equals total planned expenditure in an economy.

• Components of Expenditure: In a closed economy, the main components are:

  • Consumption (C)
  • Investment (I)

• Equilibrium Condition: The economy is in equilibrium when:

  [ Y = C + I ]

  where Y is the total output.

Step 2: Analyze the Role of Consumption

• Factors Influencing Consumption:

  • Disposable income
  • Consumer confidence
  • Interest rates

• Consumption Function: The relationship can be expressed as:

  [ C = a + bY_d ]

  where:

  • a = autonomous consumption (consumption when income is zero)
  • b = marginal propensity to consume (MPC)
  • (Y_d) = disposable income

Step 3: Examine Investment and Its Impact

• Definition of Investment: Investment refers to expenditures on capital goods that will be used for future production.

• Investment Multiplier: The multiplier effect demonstrates how an initial change in spending can lead to a larger change in overall economic output.

• Multiplier Formula: The investment multiplier is calculated as:

  [ k = \frac{1}{1 - MPC} ]

  where k is the multiplier and MPC is the marginal propensity to consume.

Step 4: Calculate the Equilibrium Output

• Determining Equilibrium Output:

  • Substitute the consumption function into the equilibrium condition.
  • Rearrange the equation to solve for Y:

  [ Y = a + bY_d + I ]

• Example Calculation:

  • If (a = 100), (b = 0.8), and (I = 50):
  • Assume (Y_d = Y) (in equilibrium).
  • Solve for Y:

  [ Y = 100 + 0.8Y + 50 ] [ 0.2Y = 150 \implies Y = 750 ]

Step 5: Identify Common Pitfalls

• Overlooking External Factors: Make sure to consider how external shocks (like changes in consumer confidence or interest rates) can affect equilibrium.
• Ignoring the Role of Savings: Remember that savings can also impact consumption and investment, thus altering your calculations.

Conclusion

In this tutorial, we explored the foundations of macroeconomic equilibrium in a closed economy without a public sector. Key takeaways include understanding the relationship between consumption and investment, calculating equilibrium output, and recognizing the significance of the investment multiplier. For further study, consider examining how these principles apply in real-world economic scenarios or in the context of open economies that include international trade.