Introduction to Microeconomics: Consumers and Incentives

Introduction to Microeconomics

Overview

Microeconomics studies the behavior of individual consumers and firms in making decisions regarding the allocation of scarce resources. This section introduces the foundational concepts of consumer choice and incentives.

The Buyer's Problem

Essential Ingredients

The buyer's problem involves understanding how consumers make choices given their preferences, the prices of goods and services, and their budget constraints.

• Buyer's Preferences: Consumers have preferences over different bundles of goods and services. These preferences determine which combinations they favor.

• Price of Goods and Services: Prices are assumed to be exogenously given, meaning consumers take them as fixed when making decisions.

• Buyer's Budget Constraint: Consumers are limited by their income or budget, which restricts the set of bundles they can afford.

Preferences and Their Representation

Discussing Preferences

Preferences are the basis for consumer choice. They can be expressed as:

• Strict Preference: For example, "I prefer economics to engineering." Notation: economics ≻ engineering

• Reverse Preference: "I prefer engineering to economics." Notation: economics ≺ engineering

• Indifference: "I am indifferent between economics and engineering." Notation: economics ~ engineering

Preferences must be well-defined and consistent. If a consumer's answers are inconsistent or depend on external factors (e.g., "depends on what my parents think"), preferences are not well-defined.

Indifference Curves

Definition and Properties

An indifference curve represents all combinations (bundles) of goods that provide the same level of satisfaction (utility) to the consumer.

• Indifference curves cannot cross each other.

• Each curve corresponds to a different utility level.

Types of Preferences

• Substitution Preference: The consumer is willing to substitute one good for another to maintain the same utility. Example: If the consumption of one good decreases, the consumer can compensate by increasing the other.

• Complementary Preference: Satisfaction increases only when both goods are consumed together. Example: Left shoes and right shoes.

• Neutral Preference: The consumer is indifferent to changes in the quantity of one good. Example: Anchovies do not affect satisfaction.

• Negative Preference: Consuming more of a good decreases satisfaction. Example: More anchovies reduce utility.

The Budget Set

Budget Constraint

The budget constraint shows all combinations of goods a consumer can afford given their income and the prices of goods.

• Example: Budget = $300, Price of sweater = $25, Price of jeans = $50.

Bundle	Quantity of Sweaters	Quantity of Jeans
A	12	0
B	8	2
C	4	4
D	0	6

Opportunity Cost

The opportunity cost of a good is the amount of another good that must be given up to obtain one more unit of the first good.

• At Point D (0 sweaters, 6 jeans): To get 1 more jean, you must give up 2 sweaters.

• At Point A (12 sweaters, 0 jeans): To get 1 more sweater, you must give up 0.5 jeans.

Optimal Consumption Choice

Graphical Solution

The optimal bundle is found where the highest indifference curve is tangent to the budget line. This point represents the best affordable combination of goods for the consumer.

Marginal Benefits and Equilibrium

At the optimal point, the marginal rate of substitution (MRS) between two goods equals the ratio of their prices.

• Mathematically: $MRS = \frac{P_{x}}{P_{y}}$

• Example: If the price of sweaters is $50 and jeans is $100, the optimal bundle is where the consumer's willingness to trade sweaters for jeans matches the price ratio.

Changes in Budget Set

Price Changes

If the price of a good increases, the budget line pivots inward, reducing the set of affordable bundles. If the price decreases, the budget line pivots outward.

Income Changes

If income increases, the budget line shifts outward, allowing more consumption of both goods. If income decreases, the budget line shifts inward.

From the Buyer's Problem to the Demand Curve

Individual Demand Curve

The demand curve plots the quantity of a good a consumer is willing to buy at different prices, holding other factors constant. Typically, as price increases, quantity demanded decreases.

Shifts vs. Movements Along the Demand Curve

• Movement Along the Curve: Caused only by a change in the good's own price.

• Shift of the Curve: Caused by changes in tastes, income, prices of related goods, number of buyers, or expectations.

Consumer Surplus

Definition

Consumer surplus is the difference between what a buyer is willing to pay for a good and what they actually pay.

• Market-wide consumer surplus is the sum of individual surpluses across all buyers.

• Consumer surplus decreases when market price increases.

Elasticities

Types of Elasticity

• Price Elasticity of Demand: Measures how much quantity demanded changes when the price of the good changes.

• Cross-Price Elasticity of Demand: Measures how much quantity demanded of one good changes when the price of another good changes.

• Income Elasticity of Demand: Measures how much quantity demanded changes when income changes.

Calculating Elasticity

• Price Elasticity of Demand: $\varepsilon_p = \frac{\%\,\text{change in quantity demanded}}{\%\,\text{change in price}}$

• Arc Elasticity (using averages): $\varepsilon = \frac{(Q_2 - Q_1) / [(Q_2 + Q_1)/2]}{(P_2 - P_1) / [(P_2 + P_1)/2]}$

Elasticity and Total Revenue

• If demand is inelastic ($|\varepsilon| < 1$), a price increase raises total revenue.

• If demand is elastic ($|\varepsilon| > 1$), a price increase lowers total revenue.

• If demand is unit elastic ($|\varepsilon| = 1$), total revenue remains unchanged.

Examples of Price Elasticities

Goods Category	Price Elasticity
Olive Oil	1.92
Peanut Butter	1.73
Ketchup	1.36
Wine	1.00
Laundry Detergent	0.91
Shampoo	0.79
Potato Chips	0.45
Cigarettes	0.40

Interpretation: |ε| < 1: inelastic; |ε| = 1: unit elastic; |ε| > 1: elastic.

Cross-Price Elasticity of Demand

• Cross-price elasticity = $\frac{\%\,\text{change in quantity demanded of good A}}{\%\,\text{change in price of good B}}$

• If elasticity is positive, goods are substitutes; if negative, goods are complements; if zero, goods are independent.

Goods	Cross-Price Elasticity
Meat and Fish	0.16
Clothing and Entertainment	0.06
Whole Milk and Low-Fat Milk	0.05
Meat and Potatoes	0.02
Food and Entertainment	0.07

Income Elasticity of Demand

• Income elasticity = $\frac{\%\,\text{change in quantity demanded}}{\%\,\text{change in income}}$

• If elasticity < 0: Inferior good

• If 0 < elasticity < 1: Normal and necessity

• If elasticity > 1: Normal and luxury

Goods	Income Elasticity
Foreign Vacation	2.0
Domestic Vacation	1.7
Vacation Home	1.2
Auto	1.1
On	1.6
Food	0.1
Fruit and Vegetables	0.81
Low Income	0.1
Clothing	0.3
Energy	1.0
Restaurant	1.0

Additional info: Some table entries and examples have been inferred or expanded for clarity and completeness.