📐 Elasticity of Demand

Demand does not always respond to price in the same way. For some goods, a small price change leads to a large change in quantity demanded. For others, demand barely moves. Elasticity measures that responsiveness.

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Meaning of Elasticity of Demand

Elasticity of demand refers to the degree of responsiveness of demand to a change in one of its determinants.

The three major forms are:

• price elasticity of demand
• income elasticity of demand
• cross elasticity of demand

Among these, price elasticity is the most commonly discussed form.

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Price Elasticity of Demand

Price elasticity of demand is the ratio of the proportionate change in quantity demanded to the proportionate change in price.

Formula:

Ep = Percentage change in quantity demanded / Percentage change in price

Because price and quantity demanded usually move in opposite directions, the value is often negative in sign, though many textbook discussions use the absolute value.

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Degrees of Price Elasticity

Perfectly Elastic Demand

• very tiny price change causes very large change in quantity demanded
• demand curve is horizontal

Elastic Demand

• percentage change in quantity demanded is greater than percentage change in price
• Ep > 1

Unitary Elastic Demand

• percentage change in quantity demanded equals percentage change in price
• Ep = 1

Inelastic Demand

• percentage change in quantity demanded is less than percentage change in price
• Ep < 1

Perfectly Inelastic Demand

• demand does not respond to price change
• demand curve is vertical

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Factors Affecting Price Elasticity

Elasticity depends on several conditions:

Availability of Substitutes

More close substitutes usually make demand more elastic.

Nature of the Commodity

Necessities tend to have inelastic demand; luxuries are usually more elastic.

Number of Uses

Goods with multiple uses often have more elastic demand.

Proportion of Income Spent

Goods that take a larger share of household income usually have more elastic demand.

Time Period

Demand is often less elastic in the short run and more elastic in the long run.

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Methods of Measuring Price Elasticity

1. Total Outlay or Total Expenditure Method

This method studies how total expenditure changes when price changes.

• if price falls and total expenditure rises, demand is elastic
• if price falls and total expenditure remains unchanged, demand is unitary elastic
• if price falls and total expenditure falls, demand is inelastic

2. Percentage Method

This is the direct formula-based method:

Ep = Percentage change in quantity demanded / Percentage change in price

3. Point Method

Used when elasticity is measured at a particular point on the demand curve.

4. Arc Method

Used when elasticity is measured between two points on a demand curve.

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Income Elasticity of Demand

Income elasticity of demand measures the responsiveness of demand to changes in income.

Formula:

Ei = Percentage change in quantity demanded / Percentage change in income

Interpretation

• positive income elasticity: demand rises as income rises
• negative income elasticity: demand falls as income rises

This helps classify goods:

• normal goods: positive income elasticity
• inferior goods: negative income elasticity

In agriculture, coarse grains may become inferior in some contexts when income rises and consumers shift toward higher-value foods.

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Cross Elasticity of Demand

Cross elasticity of demand measures how the quantity demanded of one good responds to the price change of another related good.

Formula:

Ec = Percentage change in quantity demanded of X / Percentage change in price of Y

Interpretation

• positive cross elasticity: goods are substitutes
• negative cross elasticity: goods are complements

Examples:

• tea and coffee: positive
• bread and butter: negative

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Why Elasticity Matters in Agriculture

Elasticity is important in agricultural economics because it helps explain:

• price response for staples versus high-value foods
• the effect of bumper harvests on farm revenue
• tax and subsidy incidence
• procurement and support price policy
• marketing strategy for perishables and processed foods

For example, if demand for a crop is inelastic, a large increase in production may lower price enough to reduce total farm revenue.

Summary Cheat Sheet

Topic	Quick Recall
Elasticity of demand	Responsiveness of demand to changes in determinants
Price elasticity	Response of quantity demanded to price change
Elastic demand	Ep > 1
Unitary elasticity	Ep = 1
Inelastic demand	Ep < 1
Total outlay method	Uses changes in total expenditure to infer elasticity
Income elasticity	Response of demand to income change
Cross elasticity	Response of demand for one good to price change of another
Positive cross elasticity	Substitutes
Negative cross elasticity	Complements
Agricultural relevance	Important for pricing, revenue, subsidy, and policy analysis