Equilibrium Economics

Benefits of Exchange and Economic Efficiency

• Voluntary Exchange Principle

  • All market exchanges are voluntary.
  • Voluntary exchange is based on mutual benefits; if two parties agree to trade, both parties must perceive net benefits, or else they would not engage in voluntary trade. Everyone receives a benefit.

• Components of Net Benefits

  • Consumer Surplus: The net benefit received by consumers.
  • Producer Surplus: The net benefit received by suppliers.

• Gains from Trade

  • Demand Curve (Consumers): The height of the demand curve at a given quantity represents consumers' marginal willingness to pay for that last unit, known as Marginal Value ($MV$).
  • Supply Curve (Producers): The height of the supply curve at a given quantity represents the producers' marginal cost to produce that last unit, known as Marginal Cost ($MC$).
  • Condition for Trade: If the Marginal Value to consumers exceeds the Marginal Cost to producers for a particular unit ($MV > MC$), potential gains from trade exist for both parties.
  • Exhaustion of Gains: Beneficial trades continue until Marginal Value equals Marginal Cost ($MV = MC$), at which point all gains from trade are exhausted and fully realized.

• Economic Efficiency
  • Definition: Economic efficiency occurs when all mutual benefits from trade are exhausted, where Marginal Value equals Marginal Cost ($MV = MC$).
  • Maximization of Total Surplus: At economic efficiency, net benefits to society—the sum of consumer surplus and producer surplus—are maximized.
  • Efficiency vs. Equity: Economic efficiency does not imply equity and may not always be deemed socially desirable.

Market Clearing Price and Market Equilibrium

• Market Clearing Price Definition

  • The price at which Quantity Demanded ($Q_d$) equals Quantity Supplied ($Q_s$).
  • At this price, all consumers willing to buy can find a seller, and all suppliers willing to sell can find a buyer.

• Demand and Supply Schedule

  • Demand Schedule:
  • At Price \\n - **Supply Schedule:**\n - At Price \
  • Equilibrium Point: At Price \\n\n- **Market Equilibrium Graphic Analysis**\n\n\n\n - Market equilibrium occurs at Point E, where the supply curve and the demand curve intersect.\n - Market clearing equilibrium price P^* = \$3.00$.
  • Market clearing equilibrium quantity $Q^* = 30$ units.
  • At Point $E$, all net benefits to society are maximized.

• Disequilibrium: Price Higher than Market Clearing Price

  • Scenario: Suppose the price in the market is $\\n - **Supply:** At$\
  • Demand: At $\\n - **Result:** An excess supply (Surplus) equal to$20$units ($40 - 20 = 20).\n - **Market Adjustment:** Sellers intended to sell these 20$units at$\

• Disequilibrium: Price Lower than Market Clearing Price

  • Scenario: Suppose the price in the market is $\\n - **Supply:** At$\
  • Demand: At $\\n - **Result:** An excess demand (Shortage) equal to$20$units ($40 - 20 = 20).\n - **Market Adjustment:** Suppliers find they cannot keep items in stock and can charge a higher price. Consumers who value the good more highly offer higher prices. The price gets bid up until the market clearing price of \

Market Shocks and Single Curve Shifts

• Stability of Equilibrium

  • Once at the market clearing price, there is no inherent reason for market price to change.
  • Sellers charging a higher price end up with excess supply (unsold inventory).
  • Consumers paying a lower price face excess demand (shortages).
  • Market price only changes if an exogenous shock causes the demand curve or supply curve to shift.

• Shifts of the Demand Curve

• Increase in Demand:

  • Shift: Rightward shift of the entire demand curve ($D_1 \rightarrow D_2$).
  • Movement: Movement along the same supply curve (change in quantity supplied due to price change).
  • Equilibrium Impact: Equilibrium price rises ($P_1 \rightarrow P_2$) and equilibrium quantity rises ($Q_1 \rightarrow Q_2$).

• Decrease in Demand:

  • Shift: Leftward shift of the entire demand curve.

  • Movement: Movement along the same supply curve.

  • Equilibrium Impact: Equilibrium price falls and equilibrium quantity falls.

  • Shifts of the Supply Curve

• Decrease in Supply:
  • Shift: Leftward shift of the entire supply curve ($S_1 \rightarrow S_2$).
  • Movement: Movement along the same demand curve (change in quantity demanded due to price change).
  • Equilibrium Impact: Equilibrium price rises ($P_1 \rightarrow P_2$) and equilibrium quantity falls ($Q_1 \rightarrow Q_2$).
• Increase in Supply:
  • Shift: Rightward shift of the entire supply curve.
  • Movement: Movement along the same demand curve.
  • Equilibrium Impact: Equilibrium price falls and equilibrium quantity rises.

Simultaneous Shifts of Supply and Demand

• Complex Market Shocks

  • Real-world markets often experience simultaneous shocks affecting both demand and supply.

• Analysis of Demand Increase and Supply Decrease

  • When demand increases and supply decreases simultaneously, price unambiguously increases ($P \uparrow$).
  • The impact on quantity depends on the relative magnitudes of the shifts:
  • Outcome A (Demand Shift > Supply Shift): If the rightward shift in demand is larger than the leftward shift in supply, equilibrium price rises ($P_1 \rightarrow P_2$) and equilibrium quantity rises ($Q_1 \rightarrow Q_2$).

- **Outcome B (Supply Shift > Demand Shift):** If the leftward shift in supply is larger than the rightward shift in demand, equilibrium price rises ($P_1 \rightarrow P_2$) and equilibrium quantity falls ($Q_1 \rightarrow Q_2$).

• Summary Matrix of Simultaneous Shifts

• Demand Increases & Supply Increases:
  • Price: Unknown / Ambiguous
  • Quantity: Increases
• Demand Increases & Supply Decreases:
  • Price: Increases
  • Quantity: Unknown / Ambiguous
• Demand Decreases & Supply Increases:
  • Price: Decreases
  • Quantity: Unknown / Ambiguous
• Demand Decreases & Supply Decreases:
  • Price: Unknown / Ambiguous
  • Quantity: Decreases