Elasticity of demand quantifies how much consumers adjust their purchases when an economic variable changes. The most common form, price elasticity of demand (PED), is calculated as the percentage change in quantity demanded divided by the percentage change in price. The concept was formalized by Alfred Marshall in his Principles of Economics (1890).
Economists categorize demand by the absolute value of the elasticity coefficient:
- Elastic (|E| > 1): quantity demanded responds more than proportionally to price changes. Typical of luxury goods, goods with many substitutes, or items consuming a large share of income.
- Inelastic (|E| < 1): quantity changes less than proportionally. Common for necessities, addictive goods, and products without close substitutes (insulin, gasoline in the short run, table salt).
- Unit elastic (|E| = 1): percentage changes are equal.
- Perfectly inelastic (E = 0) and perfectly elastic (E = ∞) are theoretical limits.
Other key variants include income elasticity of demand (distinguishing normal, inferior, and luxury goods) and cross-price elasticity (positive for substitutes, negative for complements).
Several factors drive elasticity: availability of substitutes, the share of income spent on the good, whether the good is a necessity or luxury, time horizon (demand becomes more elastic over longer periods as consumers adjust habits), and how narrowly the good is defined (demand for "Coca-Cola" is more elastic than demand for "soft drinks" generally).
The concept has direct policy relevance. Governments rely on inelastic demand when designing sin taxes on tobacco and alcohol, since revenue stays high even as prices rise — though the WHO and World Bank have documented that sustained tobacco tax increases do reduce consumption, especially among younger and lower-income smokers. OPEC's pricing power likewise depends on the short-run inelasticity of oil demand. Elasticity estimates also inform antitrust market-definition tests, exchange-rate pass-through analysis, and the Ramsey rule for optimal commodity taxation.
Example
When OPEC+ announced production cuts in October 2022, global oil prices rose sharply while consumption fell only modestly in the following months — a textbook illustration of inelastic short-run demand for crude oil.
Frequently asked questions
Elastic demand means quantity demanded changes by a larger percentage than price (coefficient > 1), while inelastic demand means it changes by a smaller percentage (coefficient < 1). Luxuries tend to be elastic; necessities tend to be inelastic.
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