What is Price Elasticity of Demand?
Price elasticity of demand measures the responsiveness of quantity demanded to a change in price: PED = % change in quantity demanded / % change in price. Three regions matter. Elastic (|PED| > 1): demand is price-sensitive; raising price reduces total revenue. Unit elastic (|PED| = 1): revenue unchanged. Inelastic (|PED| < 1): demand is price-insensitive; raising price increases total revenue. Elasticity depends on (1) availability of substitutes (more substitutes = more elastic), (2) necessity vs luxury, (3) share of customer budget, (4) time horizon (longer = more elastic). Insulin is highly inelastic; restaurant meals are highly elastic. Pricing decisions hinge entirely on elasticity — without estimating it, every price change is a gamble.
How Price Elasticity of Demand actually works
The framework breaks down into the following moving parts. Knowing what each piece is — and what it is not — is what separates a B-grade answer from an A-grade answer in a written assignment.
- PED = % ΔQ / % ΔP
- Elastic — raising price reduces revenue
- Inelastic — raising price increases revenue
- Drivers — substitutes, necessity, budget share, time
- Estimate via experiments, conjoint, historical analysis
A worked example: Insulin pricing
Insulin is one of the most inelastic products in healthcare — diabetics cannot substitute or skip doses, so demand barely falls even when price rises. Eli Lilly raised insulin prices by 5x between 2001 and 2017 with minimal volume loss; total revenue grew accordingly. The inelasticity drove Congressional investigations and eventually federal price caps in 2023. The case shows both the economic power of pricing inelastic goods and the regulatory backlash when essential goods are priced inelastically. By contrast, restaurant dining is highly elastic — modest price increases produce significant volume drop, which is why restaurants are reluctant to raise prices and instead reduce portion sizes or surcharge through "service fees."
Don't lose marks for these
- Treating elasticity as constant (it varies with time and segment)
- Pricing without estimating elasticity
- Assuming inelastic markets stay inelastic (substitutes emerge)
How to use this on the exam
Score-maximizing moves
- Show the formula
- Distinguish elastic, unit, inelastic
- Cite drivers of elasticity
When to use Price Elasticity of Demand (and when not to)
Use Price Elasticity of Demand when your assignment asks you to analyze, structure, or recommend — and when you have at least two data points to populate every cell of the framework. Skip it when the question is asking for a numerical answer or a single recommendation, since Price Elasticity of Demand is a structuring tool, not a calculator.