Macroeconomics Notes

Macroeconomic Equilibrium

• This section discusses macroeconomic equilibrium, focusing on how to measure and analyze the overall economy.

Key Concepts

• National Income Equilibrium: The point where aggregate demand equals aggregate supply.
• Leakages (W): Withdrawals of money from the circular flow of income (savings, taxes, and imports).
• Injections (J): Additions of money into the circular flow of income (investment, government spending, and exports).

National Income and Expenditure

• National income can be measured using the expenditure approach: $Y = C + I + G + NX$ where:
  • $Y$ = National Income
  • $C$ = Consumption
  • $I$ = Investment
  • $G$ = Government Spending
  • $NX$ = Net Exports (Exports - Imports)

Components of Aggregate Expenditure

1. Consumption (C): Spending by households on goods and services. It's a major driver of economic activity.
   • Influenced by disposable income.
   • A significant portion is spent on essential items.
   • It is the largest component of aggregate expenditure. Consumption is determined by disposable income, where an increase in income generally leads to increased consumption.

Equilibrium Condition

• Equilibrium occurs when total leakages equal total injections: $W = J$
  • $S + T + M = I + G + X$
  • Savings (S) + Taxes (T) + Imports (M) = Investment (I) + Government Spending (G) + Exports (X)

Consumption Function

• The consumption function relates consumption expenditure to disposable income.
• Equation: $C = a + bY_d$
  • $C$ = Consumption
  • $a$ = Autonomous Consumption (consumption independent of income)
  • $b$ = Marginal Propensity to Consume (MPC)
  • $Y_d$ = Disposable Income
• MPC (Marginal Propensity to Consume): change in consumption / change in disposable income $\frac{\Delta C}{\Delta Y_d}$

Savings Function

• Relates savings to disposable income.
• Equation: $S = -a + (1-b)Y_d$
  • $-a$ = Dissaving (when consumption exceeds income)
  • $(1-b)$ = Marginal Propensity to Save (MPS)
• MPS (Marginal Propensity to Save) = change in savings / change in disposable income $\frac{\Delta S}{\Delta Y_d}$

Key Relationships

• $MPC + MPS = 1$
• $APC + APS = 1$
  • APC (Average Propensity to Consume) = $\frac{C}{Y_d}$
  • APS (Average Propensity to Save) = $\frac{S}{Y_d}$

Important Considerations

• As disposable income increases, the MPC generally decreases while the MPS increases.
• In a basic macroeconomic model, autonomous consumption ($a$) should be greater than zero.

Investment Expenditure (I)

• Investment includes spending on new plants, equipment, and inventory.
• It is a crucial injection into the economy.
• Fluctuations in investment can significantly impact economic output.

Simple Model

• Model: $Y = C + I$
• Where:
  • $C = 450 + 0.6Y$
  • $I = 150$
• Equilibrium Condition: $Y = E$
  • $Y = 450 + 0.6Y + 150$
  • $0.4Y = 600$
  • $Y = 1500$
• Leakages and Injections: $W = J$
  • $-450 + 0.4Y = 150$
  • $0.4Y = 600$
  • $Y = 1500$
• Consumption = 450 + 0.6Y, savings = −450 + 0.4Y.

Graphical Representation

• The equilibrium point can be shown graphically where the aggregate expenditure line intersects the 45-degree line.

Government Sector

• Introducing government spending (G) and taxes (T) to the model.

New Variables

• Net Taxes (NT = Taxes - Transfers).
• Disposable Income (Yd = Y - NT).
• New Equilibrium Condition: $Y = C + I + G$
• Which can be written as $Y = C + S + NT$
• Therefore at equilibrium: $C + I + G = C + S + NT$
• $I + G = S + NT$
• Leakages (W) = $S + NT$
• Injections (J) = $I + G$

Disposable income

• $Y_d = Y - NT$

Multipliers

Simple Multiplier

• $K = \frac{1}{1-MPC} = \frac{1}{MPS}$

With Income Tax

• $K = \frac{1}{MPS + MPT}$

Interpretation

• The multiplier effect shows how a change in autonomous expenditure can lead to a larger change in national income.
• Example: If investment increases by $x$, national income increases by a multiple of $x$.

Open Economy

• In an open economy, trade and international capital flows are considered.

Additional Variables

• Exports (X) and Imports (M).
• Net Exports (NX = X - M).

Equilibrium Condition

• $Y = C + I + G + NX$
• Since $Y = C + S + NT$
• and $E = C + I + G + NX$
• At equilibrium $C + S + NT + M = C + I + G + X$
• Therefore $S + NT + M = I + G + X$
• Leakages = $S + NT + M$
• Injections = $I + G + X$