Microeconomics Study Notes: Elasticity, Surplus, Taxation, and Consumer Choice

Economic Surplus and Taxation

Consumer and Producer Surplus

Economic surplus is a key concept in microeconomics, representing the total benefit to society from the production and consumption of goods and services. It is divided into consumer surplus and producer surplus.

• Consumer Surplus: The difference between what consumers are willing to pay for a good and what they actually pay. Formula: Consumer Surplus = Perceived Value - Price

• Producer Surplus: The difference between the price producers receive and the minimum price at which they are willing to sell.

• Total Surplus: The sum of consumer and producer surplus.

Total Surplus = Consumer Surplus + Producer Surplus

Taxation and Welfare Effects

Taxes affect market outcomes by creating a wedge between the price buyers pay and the price sellers receive, leading to changes in consumer and producer surplus.

• Unit Tax: A fixed amount of tax per unit sold, regardless of price.

• Ad Valorem Tax: A tax that is a percentage of the price of the good.

• Consumer Incidence: The portion of the tax paid by consumers (reflected in higher prices).

• Producer Incidence: The portion of the tax paid by producers (reflected in lower received prices).

Graphical analysis shows the welfare effect of a tax:

• Before tax: Larger consumer and producer surplus.

• After tax: Surplus is reduced, and a portion is transferred to the government as tax revenue. Deadweight loss represents the lost surplus due to reduced quantity traded.

Tax Amount	Consumer Incidence	Producer Incidence
Unit/Ad Valorem	Change in consumer price due to tax	Change in producer price due to tax

Tax Revenue = Tax × Quantity Sold (collected by government)

Deadweight Loss = Old Surplus - New Surplus

Elasticity

Price Elasticity of Demand

Elasticity measures how much one economic variable responds to changes in another. Price elasticity of demand quantifies how much the quantity demanded of a good responds to changes in its price.

• Elastic Demand: Quantity demanded changes by a larger percentage than price.

• Inelastic Demand: Quantity demanded changes by a smaller percentage than price.

• Unit Elastic Demand: Percentage change in quantity demanded equals percentage change in price.

Price Elasticity of Demand (Midpoint Formula):

$ext{P.E.O.D.} = \frac{(Q_2 - Q_1)}{(Q_2 + Q_1)/2} \div \frac{(P_2 - P_1)}{(P_2 + P_1)/2}$

• All demand curves have an elastic and inelastic portion separated by a point of unit elasticity.

Special Cases

• Perfectly Inelastic Demand: Quantity demanded does not change as price changes ($E_d = 0$).

• Perfectly Elastic Demand: Quantity demanded is infinitely responsive to price ($E_d = \infty$).

Determinants of Price Elasticity of Demand

• Availability of substitutes: More substitutes, more elastic demand.

• Time horizon: Demand becomes more elastic over time.

• Luxury vs. necessity: Luxury goods have more elastic demand.

• Definition of market: Narrowly defined markets have more elastic demand.

• Share of budget: Goods that take a larger share of the budget have more elastic demand.

Elastic Demand and Revenue

• If price increases and demand is elastic, total revenue falls.

• If price increases and demand is inelastic, total revenue rises.

Cross-Price Elasticity of Demand

Measures the responsiveness of quantity demanded of one good to changes in the price of another good.

Cross-Price Elasticity of Demand:

$\text{C.P.E.O.D.} = \frac{(Q_{A2} - Q_{A1})}{(Q_{A2} + Q_{A1})/2} \div \frac{(P_{B2} - P_{B1})}{(P_{B2} + P_{B1})/2}$

• If cross-price elasticity = 0: No relationship between goods.

• If cross-price elasticity > 0: Goods are substitutes.

• If cross-price elasticity < 0: Goods are complements.

Income Elasticity of Demand

Measures the responsiveness of quantity demanded to changes in consumer income.

• Income Elasticity > 1: Luxury goods (quantity demanded increases more than income).

• Income Elasticity < 1: Necessity goods (quantity demanded increases less than income).

• Income Elasticity < 0: Inferior goods (quantity demanded decreases as income rises).

Income Elasticity of Demand:

$\text{Income Elasticity} = \frac{\% \Delta Q}{\% \Delta I}$

Price Elasticity of Supply

Measures the responsiveness of quantity supplied to changes in price.

Price Elasticity of Supply:

$\text{P.E.O.S.} = \frac{(Q_2 - Q_1)}{(Q_2 + Q_1)/2} \div \frac{(P_2 - P_1)}{(P_2 + P_1)/2}$

• If inputs are easy to obtain, supply is more elastic.

• If inputs are difficult to obtain, supply is less elastic.

• Supply is less elastic in the short term and more elastic in the long term.

Consumer Choice and Utility

Utility and Marginal Utility

Utility is the satisfaction or benefit derived from consuming goods and services. Marginal utility is the additional satisfaction gained from consuming one more unit of a good.

• Marginal Utility (MU): Change in total utility from consuming an additional unit.

• Law of Diminishing Marginal Utility: As more units are consumed, the additional satisfaction from each unit decreases.

Marginal Utility per Dollar: Consumers maximize utility when the marginal utility per dollar spent is equal across all goods.

$\frac{MU_A}{P_A} = \frac{MU_B}{P_B}$

Budget Constraint and Income Effect

• Budget Constraint: The limited amount of income available to spend on goods and services.

• Income Effect: Change in quantity demanded due to a change in consumer purchasing power.

• Substitution Effect: Change in quantity demanded due to a change in relative prices, holding purchasing power constant.

Indifference Curves and Marginal Rate of Substitution

• Indifference Curve: A curve showing combinations of goods that provide the same level of utility to the consumer.

• Marginal Rate of Substitution (MRS): The rate at which a consumer is willing to trade one good for another while remaining equally satisfied.

Indifference curves are typically convex to the origin, reflecting diminishing MRS.

Term	Definition
Budget Constraint	Limited income for spending on goods/services
Income Effect	Change in quantity demanded due to change in purchasing power
Substitution Effect	Change in quantity demanded due to change in relative prices
Indifference Curve	Combinations of goods yielding equal utility
MRS	Rate of trade-off between goods for equal satisfaction

Additional info:

• Some definitions and formulas were expanded for clarity and completeness.

• Examples and graphical references were described in text for accessibility.