Elasticity: The Responsiveness of Demand and Supply (Microeconomics Chapter 6 Study Notes)

Elasticity: The Responsiveness of Demand and Supply

Introduction

Elasticity is a central concept in microeconomics, measuring how much one economic variable responds to changes in another. In this chapter, we focus on the responsiveness of demand and supply to changes in price and other factors, providing tools for analyzing consumer and producer behavior.

6.1 The Price Elasticity of Demand and Its Measurement

Definition and Calculation

• Price elasticity of demand quantifies how much the quantity demanded of a good responds to a change in its price.

• Formula: $\text{Price elasticity of demand} = \frac{\text{Percentage change in quantity demanded}}{\text{Percentage change in price}}$

• Elasticity is based on percentage changes, not absolute changes, making it unit-free and comparable across goods.

Midpoint Formula

• To avoid ambiguity in percentage change calculations, use the midpoint formula: $\text{Percentage change} = \frac{A - B}{(A + B)/2}$

• For elasticity: $\text{Price elasticity of demand} = \frac{Q_2 - Q_1}{(Q_2 + Q_1)/2} \div \frac{P_2 - P_1}{(P_2 + P_1)/2}$

Elasticity Terminology

• Elastic demand: Absolute value of elasticity > 1. Quantity demanded changes more than price.

• Inelastic demand: Absolute value of elasticity < 1. Quantity demanded changes less than price.

• Unit elastic demand: Absolute value of elasticity = 1. Quantity and price change by the same percentage.

Examples

• If a 10% increase in price leads to a 15% decrease in quantity demanded, demand is elastic.

• If a 10% increase in price leads to a 5% decrease in quantity demanded, demand is inelastic.

6.2 The Determinants of the Price Elasticity of Demand

Key Determinants

• Availability of close substitutes: More substitutes make demand more elastic.

• Passage of time: Elasticity increases over time as consumers adjust.

• Luxury vs. necessity: Luxuries have more elastic demand than necessities.

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

• Share of a good in a consumer's budget: Goods that take up a large budget share have more elastic demand.

6.3 The Relationship between Price Elasticity of Demand and Total Revenue

Total Revenue

• Total revenue is calculated as: $\text{Total revenue} = \text{Price} \times \text{Quantity sold}$

• When demand is elastic, lowering price increases total revenue.

• When demand is inelastic, lowering price decreases total revenue.

• When demand is unit elastic, total revenue remains unchanged as price changes.

HTML Table: Relationship between Price Elasticity and Revenue

If demand is...	then...	because...
Elastic	Increase in price reduces revenue	Quantity demanded falls proportionally more than price rises
Elastic	Decrease in price increases revenue	Quantity demanded rises proportionally more than price falls
Inelastic	Increase in price increases revenue	Quantity demanded falls proportionally less than price rises
Inelastic	Decrease in price reduces revenue	Quantity demanded rises proportionally less than price falls
Unit elastic	Price changes do not affect revenue	Quantity demanded changes by the same percentage as price

6.4 Other Demand Elasticities

Cross-Price Elasticity of Demand

• Measures how the quantity demanded of one good responds to a change in the price of another good.

• Formula: $\text{Cross-price elasticity of demand} = \frac{\text{Percentage change in quantity demanded of Good A}}{\text{Percentage change in price of Good B}}$

• Positive value: Goods are substitutes. Negative value: Goods are complements.

Income Elasticity of Demand

• Measures how the quantity demanded responds to changes in consumer income.

• Formula: $\text{Income elasticity of demand} = \frac{\text{Percentage change in quantity demanded}}{\text{Percentage change in income}}$

• Positive value: Normal good. Negative value: Inferior good.

6.5 Using Elasticity to Analyze the Disappearing Family Farm

Application of Elasticity Concepts

• Productivity gains in farming increase supply, but if demand is inelastic and income elasticity is low, prices fall sharply and total revenue may decrease.

• This explains why fewer people choose to farm despite higher productivity.

6.6 The Price Elasticity of Supply and Its Measurement

Definition and Calculation

• Price elasticity of supply measures how much the quantity supplied responds to a change in price.

• Formula: $\text{Price elasticity of supply} = \frac{\text{Percentage change in quantity supplied}}{\text{Percentage change in price}}$

• Calculation methods are analogous to those for demand elasticity (including midpoint formula).

Determinants of Price Elasticity of Supply

• Time period: Supply is more elastic in the long run than in the short run.

• Ability to alter production: If firms can easily change output, supply is more elastic.

Polar Cases

• Perfectly inelastic supply: Quantity supplied does not respond to price changes (vertical supply curve, elasticity = 0).

• Perfectly elastic supply: Quantity supplied is infinitely responsive to price changes (horizontal supply curve, elasticity = infinity).

HTML Table: Summary of Price Elasticity of Demand

If demand is...	Absolute value of price elasticity is...	Example
Elastic	Greater than 1	10% price increase causes >10% decrease in quantity demanded
Inelastic	Less than 1	10% price increase causes <10% decrease in quantity demanded
Unit elastic	Equal to 1	10% price increase causes 10% decrease in quantity demanded
Perfectly elastic	Infinity	Any price increase causes quantity demanded to fall to zero
Perfectly inelastic	Zero	Price changes do not affect quantity demanded

Conclusion

Elasticity is a powerful tool for understanding market behavior, pricing strategies, and the effects of policy changes. By mastering the concepts and calculations of elasticity, students can analyze real-world economic issues with greater precision.