Elasticity

Introduction to Elasticity

Elasticity is a fundamental concept in microeconomics that measures how much one variable responds to changes in another variable. The most common applications are the price elasticity of demand and supply, which quantify how quantity demanded or supplied responds to changes in price.

• Elasticity is always expressed as a percentage change, making it unit-free and comparable across different goods and markets.

• Elasticity helps policymakers and businesses predict the effects of price changes, taxes, and other interventions.

Price Elasticity of Demand

Definition and Calculation

The price elasticity of demand measures the responsiveness of quantity demanded to a change in price along the demand curve.

• Formula:

• Where is the percentage change in quantity demanded and is the percentage change in price.

• Elasticity is usually negative due to the Law of Demand, but the absolute value is often used for classification.

• Elasticity is related to the slope of the demand curve:

• Where and are the average price and quantity over the interval considered.

Examples and Units

• Changing the units of measurement (e.g., bottles vs. six-packs) does not affect elasticity, only the slope.

• Elasticity is a unit-free measure, making it ideal for comparisons.

Classification of Elasticity

Elasticity values are classified as follows:

Determinants of Demand Elasticity

• Availability of close substitutes (e.g., medicine vs. collectibles)

• Proportion of income spent on the good (e.g., transit vs. cars)

• Time horizon (elasticity is higher in the long run as consumers adjust)

Elasticity and Revenue

Total Revenue and Expenditure

Total revenue (or expenditure) is the product of price and quantity:

• How revenue changes with price depends on the price elasticity of demand.

Effect of Elasticity on Revenue

• If demand is elastic, a price increase reduces total revenue.

• If demand is inelastic, a price increase raises total revenue.

Other Demand Elasticities

Income Elasticity of Demand

The income elasticity of demand measures how quantity demanded responds to changes in consumer income.

• If , the good is a normal income-elastic good (luxury).

• If , the good is a normal income-inelastic good (necessity).

• If , the good is an inferior good (demand falls as income rises).

Cross-Price Elasticity of Demand

The cross-price elasticity of demand measures how the quantity demanded of one good responds to a change in the price of another good.

• Positive for substitutes (e.g., butter and margarine).

• Negative for complements (e.g., coffee and sugar).

Price Elasticity of Supply

Definition and Calculation

The price elasticity of supply measures the responsiveness of quantity supplied to a change in price along the supply curve.

• Usually positive, reflecting the Law of Supply.

Classification of Supply Elasticity

Determinants of Supply Elasticity

• Availability of close production substitutes (e.g., cornfields vs. oil refineries)

• Financial flexibility of firms (e.g., family-owned vs. international chains)

• Time frame (supply is more elastic in the long run as firms adjust production)

Estimating Elasticities

Data and Methods

• Elasticities are estimated using observed data on prices and quantities over time.

• Ideal estimation uses random experiments or natural quasi-experiments (e.g., supply shifters like input costs).

• Econometric methods are used for more advanced estimation (covered in higher-level courses).

Summary Table: Demand and Supply Elasticities

Additional info:

• Elasticity is a central tool for analyzing the effects of policies such as taxes, subsidies, and price controls.

• Understanding elasticity helps explain why some policies have unintended consequences or are less effective than intended.