econ 10/8

Keynesian Economic Model

• The Keynesian model seeks to explain how the economy can be in a short-term disequilibrium.
  • Disequilibrium defined as a state where the market is not at the classical full equilibrium point.
  • Proposed by John Maynard Keynes to show how high unemployment and low employment can persist without intervention.

Components of GDP

• The model is based on the expenditure approach to calculating GDP which is represented as:
  • $GDP = C + I + G + NX$
  • Where:
    • $C$ = Consumption
    • $I$ = Investment
    • $G$ = Government Spending
    • $NX$ = Net Exports
• All values are measured in real terms, meaning price changes are not considered until a later chapter.

Multiplier Effect

• The concept of the multiplier explains how changes in one of the GDP components (C, I, G, or NX) can lead to greater overall economic change.
  • Definition: The multiplier indicates that if government spending, consumption, or investment increases, this will inject more money into the economy.
  • An extra dollar of income signifies an extra dollar of spending for someone else, leading to a multiplication effect through the economy.
• The amount of income that is spent is determined by the marginal propensity to consume (MPC), and the amount saved is determined by the marginal propensity to save (MPS).
  • $MPS = 1 - MPC$
• The cycle causes continuous new spending, promoting overall economic activity.

Dependency Variables in Economic Activity

• Consumption is dependent on disposable income.
• Investment depends on interest rates.
• Government spending is considered constant for analysis purposes, noted with a bar over it as a fixed variable alongside net exports, which depend on exchange rates.

Deriving Multiplier and Equilibrium

• Equilibrium Analysis: In short-term equilibrium, aggregate expenditures (AE) are equal to income (Y).
• To derive the equations:
  • Substitute functions related to consumption into the aggregate expenditure formula.
  • Assume a linear consumption function: $C = a + b(Y - T)$
  • Where $a$ represents autonomous consumption, $b$ is the MPC, $Y$ is income, and $T$ is taxes.
• Rearranging yields:
  • Collecting all terms gives the equation for equilibrium.
• The general formula for the multiplier indicating the effect of spending on GDP is:
  • $Multiplier = \frac{1}{1 - MPC}$
  • This implies that for every increase in government spending, income increases by a greater factor due to the multiplier effect, given that 0 < MPC < 1.
• The tax multiplier can be derived similarly, indicating that changes in taxes negatively impact consumption and disposable income leading to a multiplier effect on GDP.
• Tax Multiplier Formula:
  • Negative sign emphasizes the inverse relationship.

Changes in Equilibrium and Logical Flow

• Changes in the equilibrium can be examined through the delta (Δ) symbol which represents a change in a variable:
  • $ΔY = \frac{1}{1 - MPC}(ΔI + ΔG + ΔNX) + (Tax ext{ }Multiplier)(ΔT)$
• Understanding logical flows in economics is crucial, recognizing that adverse changes (e.g., increased taxes) lead to decreased consumption:
  • Increased taxes lead to a decrease in disposable income, causing reduced overall economic activity.

Current Economic Context and Investment Dynamics

• The economy is experiencing an increase in investment driven by AI growth, influencing overall GDP positively despite weak consumer spending.
  • Investment contributes significantly to GDP as it translates to increased production capacity and expenditure.
  • Relationships to stock market dynamics are observed where investment in tech (notably AI sectors) is correlated with GDP growth.

Business Cycle Phases

• The business cycle consists of several phases, including:
  • Peak
  • Recession
  • Trough
  • Expansion.
• The role of government intervention during economic downturns is emphasized:
  • Keynes argues for active government involvement to address recessions, contrasting classical views that suggest a hands-off approach.
• Recessionary and Inflationary Gaps:
  • A recessionary gap occurs when actual GDP is below potential GDP, leading to unemployment and idle resources.
  • An inflationary gap occurs when actual GDP exceeds potential GDP, causing inflation as demand pressures exceed supply.
• Examples in response to output variations indicate that:
  • An increase in government spending has a multiply effect on GDP depending on existing economic conditions.

Economic Responses and Policy Implications

• Keynes identified that insufficient aggregate demand could lead to recessionary conditions marked by high unemployment and deflationary pressures.
• Suggested policy responses include expansionary fiscal and monetary policy:
  • Expansionary fiscal policies like increased government spending or reduced taxes.
  • Monetary policies increasing the money supply or lowering interest rates to stimulate investment.
• Conversely, for inflationary gaps, contractionary measures are warranted:
  • Contractionary policy responses: Increasing taxes to reduce spending or engaging in tighter monetary policy, such as raising interest rates, which reduces investment and overall economic activity.

Key Definitions

• Inflationary Gap: When actual real GDP exceeds potential GDP, resulting in undue pressure to produce more than the economy's capacity.
• Recessionary Gap: When actual real GDP is below the economy's full employment level, leading to rising unemployment and unused resources.