Elasticity: The Responsiveness of Demand and Supply

Introduction to Elasticity

Elasticity is a fundamental concept in microeconomics that measures how much one economic variable responds to changes in another. It is especially important for understanding consumer and producer behavior in response to price changes, and for evaluating the effects of policies such as taxes.

• Elasticity: A measure of responsiveness, typically expressed as a percentage change in one variable resulting from a percentage change in another variable.

• Common applications include analyzing the effects of taxes, predicting changes in revenue, and understanding market dynamics.

• Example: Soda taxes are used to reduce sugar consumption and raise public funds. The actual effect depends on how responsive consumers are to price changes (i.e., the price elasticity of demand).

Price Elasticity of Demand

Definition and Measurement

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

• Price Elasticity of Demand: The percentage change in quantity demanded divided by the percentage change in price.

• The value is typically negative due to the inverse relationship between price and quantity demanded, but the absolute value is often used for interpretation.

• The slope of the demand curve and elasticity are related but not the same; elasticity uses percentage changes, making it unit-free and comparable across goods.

Elasticity Terminology

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

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

• Unit-Elastic Demand: Elasticity = 1. Quantity demanded changes exactly proportionally to price changes.

• Perfectly Inelastic Demand: Elasticity = 0. Quantity demanded does not change as price changes (vertical demand curve).

• Perfectly Elastic Demand: Elasticity = ∞. Quantity demanded is infinitely responsive to price (horizontal demand curve).

Calculating Elasticity: The Midpoint Formula

To avoid inconsistencies in percentage change calculations, the midpoint formula is used:

• This formula ensures the elasticity value is the same regardless of the direction of the change.

Graphical Illustration: Elastic vs. Inelastic Demand

• On a demand curve, a price cut from $1.50 to $1.35 may increase quantity sold from 1,000 to 1,200 (elastic) or only to 1,050 (inelastic), depending on the curve's steepness.

• Elastic demand curves are flatter; inelastic demand curves are steeper.

Summary Table: Price Elasticity of Demand

Determinants of Price Elasticity of Demand

Several factors influence how elastic the demand for a good is:

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

• Passage of Time: Demand is more elastic in the long run as consumers adjust.

• Luxury vs. Necessity: Luxuries have more elastic demand; necessities are inelastic.

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

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

Elasticity and Total Revenue

Total revenue is the product of price and quantity sold. The effect of a price change on total revenue depends on the price elasticity of demand.

• Total Revenue (TR):

• If demand is elastic, a price decrease increases total revenue.

• If demand is inelastic, a price decrease decreases total revenue.

• If demand is unit-elastic, total revenue does not change with price.

Other Demand Elasticities

Cross-Price Elasticity of Demand

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

Income Elasticity of Demand

Measures the responsiveness of quantity demanded to changes in income.

Price Elasticity of Supply

Definition and Measurement

The price elasticity of supply measures how much the quantity supplied of a good responds to a change in its price.

• Calculated similarly to price elasticity of demand, often using the midpoint formula.

Determinants of Price Elasticity of Supply

• Time Period: Supply is more elastic in the long run as producers can adjust production.

• Flexibility of Production: The easier it is to increase output, the more elastic supply is.

Special Cases

• Perfectly Inelastic Supply: Vertical supply curve; elasticity = 0. Example: Fixed number of parking spaces.

• Perfectly Elastic Supply: Horizontal supply curve; elasticity = ∞. Example: Long-run agricultural supply.

Elasticity and Market Outcomes

• When demand increases, the effect on equilibrium price depends on the elasticity of supply.

• If supply is inelastic, price rises significantly; if supply is elastic, price rises less.

Summary of Key Elasticity Formulas

• Price Elasticity of Demand:

• Cross-Price Elasticity of Demand:

• Income Elasticity of Demand:

• Price Elasticity of Supply: