Microeconomics Study Guide: Elasticity, Surplus, Taxation, Trade, and Externalities

Elasticity of Demand

Price Elasticity of Demand

The price elasticity of demand measures how much the quantity demanded of a good responds to a change in its price. It is a key concept in microeconomics for understanding consumer behavior and market dynamics.

• Definition: The percentage change in quantity demanded divided by the percentage change in price.

• Formula: $\text{Price Elasticity of Demand} = \frac{\%\ \text{Change in Quantity Demanded}}{\%\ \text{Change in Price}}$

• Midpoint (Arc) Formula: Used to calculate elasticity between two points: $\text{Elasticity} = \frac{(Q_2 - Q_1)/[(Q_2 + Q_1)/2]}{(P_2 - P_1)/[(P_2 + P_1)/2]}$

• Factors Affecting Elasticity:

  • Availability of substitutes

  • Necessity vs. luxury

  • Proportion of income spent on the good

  • Time horizon (elasticity increases over time)

• Types of Elasticity:

  • Elastic (>1): Quantity demanded changes more than price

  • Inelastic (<1): Quantity demanded changes less than price

  • Unit elastic (=1): Proportional change

• Cross-Price Elasticity of Demand: Measures the responsiveness of demand for one good to a change in the price of another good. $\text{Cross-Price Elasticity} = \frac{\%\ \text{Change in Quantity Demanded of Good A}}{\%\ \text{Change in Price of Good B}}$

  • Positive for substitutes

  • Negative for complements

  • Zero for unrelated goods

Example: If the price of coffee increases by 10% and the quantity demanded falls by 20%, the price elasticity is -2 (elastic demand).

Consumer and Producer Surplus

Definition and Allocation of Resources

Consumer surplus is the difference between what consumers are willing to pay and what they actually pay. Producer surplus is the difference between the price producers receive and the minimum they are willing to accept.

• Efficient Allocation: Achieved when total surplus (consumer + producer) is maximized.

• Market Equilibrium: The point where supply equals demand, maximizing total surplus.

• Over- and Underproduction: Overproduction leads to wasted resources; underproduction leads to missed opportunities for gains from trade.

Example: If a buyer is willing to pay $10 for a good but pays $7, their consumer surplus is $3.

Price Controls and Market Outcomes

Price Ceilings and Floors

Price controls are government-imposed limits on prices in the market.

• Price Ceiling: Maximum legal price (e.g., rent control). If set below equilibrium, causes shortages.

• Price Floor: Minimum legal price (e.g., minimum wage). If set above equilibrium, causes surpluses.

• Effects: Deadweight loss, black markets, changes in surplus.

Example: A minimum wage above equilibrium wage creates unemployment (labor surplus).

Taxation and Its Effects

Tax Incidence and Burden

Tax incidence refers to how the burden of a tax is distributed between buyers and sellers.

• Incidence: Determined by relative elasticities of supply and demand.

• Burden: The side of the market (buyers or sellers) that is less elastic bears more of the tax burden.

• Types of Taxes:

  • Progressive: Higher income pays higher percentage

  • Regressive: Lower income pays higher percentage

  • Proportional: Same percentage for all

• Income Tax vs. Sales Tax: Income tax is based on earnings; sales tax is based on purchases.

Example: If demand is inelastic and supply is elastic, consumers bear most of the tax burden.

International Trade and Comparative Advantage

Comparative Advantage and Trade Barriers

Comparative advantage is the ability to produce a good at a lower opportunity cost than others. Trade allows countries to specialize and gain from exchange.

• Comparative vs. Absolute Advantage: Absolute advantage is producing more with the same resources; comparative is lower opportunity cost.

• Trade Barriers:

  • Tariffs: Taxes on imports

  • Quotas: Limits on quantity

  • Voluntary Export Restraints (VER): Exporting country limits exports

• Effects: Trade barriers raise prices, reduce consumer surplus, and create deadweight loss.

Example: If Country A can produce wine at a lower opportunity cost than cheese, it should specialize in wine and trade for cheese.

Externalities and Social Costs

Externalities and Public Policy

An externality is a cost or benefit that affects a third party not directly involved in a transaction. Externalities can be positive (benefits) or negative (costs).

• Marginal Social Benefit (MSB): The total benefit to society from consuming one more unit.

• Marginal Social Cost (MSC): The total cost to society from producing one more unit.

• Social Optimum: Achieved when MSB = MSC.

• Coase Theorem: If property rights are well-defined and transaction costs are low, private bargaining can solve externality problems.

• Government Solutions: Taxes, subsidies, regulation, tradable permits.

Example: Pollution from a factory imposes a negative externality on nearby residents; a tax equal to the external cost can internalize the externality.

Summary Table: Key Microeconomic Concepts

Concept	Definition	Example
Price Elasticity of Demand	Responsiveness of quantity demanded to price changes	Luxury goods have high elasticity
Consumer Surplus	Difference between willingness to pay and actual price	Paying $7 for a good valued at $10
Tax Incidence	Distribution of tax burden between buyers and sellers	Gasoline taxes often fall on consumers
Comparative Advantage	Lower opportunity cost in production	Country A specializes in wine, Country B in cheese
Externality	Uncompensated impact on third parties	Pollution, vaccinations