Define price elasticity of demand. Explain the types of price elasticity of demand. [3+7]

Price Elasticity of Demand (PED)

Definition

Price elasticity of demand (PED) measures the responsiveness of the quantity demanded of a good to a change in its price, ceteris paribus (all other factors remaining constant). Mathematically, it is defined as:

$$E_d=\frac{\%\text{ Change in Quantity Demanded}}{\%\text{ Change in Price}}$$

If the percentage change in quantity demanded is greater than the percentage change in price, demand is elastic. If it is less, demand is inelastic. If they are equal, demand is unitary elastic.

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Types of Price Elasticity of Demand

Price elasticity of demand can be classified into five main types, each representing a different degree of responsiveness of demand to price changes. These are:

1. Perfectly Elastic Demand (E_d = ∞)
2. Relatively Elastic Demand (E_d > 1)
3. Unitary Elastic Demand (E_d = 1)
4. Relatively Inelastic Demand (E_d < 1)
5. Perfectly Inelastic Demand (E_d = 0)

Each type is explained below with graphical and numerical illustrations.

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1. Perfectly Elastic Demand (E_d = ∞)

• Definition: Demand is perfectly elastic when consumers are extremely sensitive to price changes. Even a tiny increase in price leads to zero demand, while any decrease in price leads to infinite demand.
• Graphical Representation: The demand curve is a horizontal line parallel to the x-axis.
• Example: Agricultural products in a perfectly competitive market (e.g., wheat in a large market where buyers have many substitutes).
• Implication: Firms must sell at the market price; they cannot charge a higher price.

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2. Relatively Elastic Demand (E_d > 1)

• Definition: Demand is relatively elastic when the percentage change in quantity demanded is greater than the percentage change in price. This means consumers are highly responsive to price changes.
• Graphical Representation: The demand curve is steeply sloped (flatter than unitary elastic).
• Example: Luxury goods (e.g., designer clothes, vacations).
• Implication: A small price increase leads to a large decrease in demand, increasing total revenue.

Numerical Example:

• Initial Price (P₁) = Rs. 100, Initial Quantity (Q₁) = 50 units
• New Price (P₂) = Rs. 120, New Quantity (Q₂) = 30 units

$$E_d=\frac{\%\Delta Q_d}{\%\Delta P}=\frac{\frac{30-50}{50}}{\frac{120-100}{100}}=\frac{-0.4}{0.2}=-2(\text{Elastic, }|E_d|>1)$$

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3. Unitary Elastic Demand (E_d = 1)

• Definition: Demand is unitary elastic when the percentage change in quantity demanded is equal to the percentage change in price. Total revenue remains constant despite price changes.
• Graphical Representation: The demand curve is a rectangular hyperbola (a curve that forms a right angle with the axes).
• Example: Some branded products where consumers adjust quantity proportionally to price changes.
• Implication: Firms cannot increase total revenue by changing price; they must rely on other strategies (e.g., advertising).

Numerical Example:

• Initial Price (P₁) = Rs. 50, Initial Quantity (Q₁) = 40 units
• New Price (P₂) = Rs. 60, New Quantity (Q₂) = 30 units

$$E_d=\frac{\frac{30-40}{40}}{\frac{60-50}{50}}=\frac{-0.25}{0.2}=-1.25(\text{Approximately unitary if }{E}_d=-1)$$

(Note: For exact unitary elasticity, the percentage changes must be equal.)

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4. Relatively Inelastic Demand (E_d < 1)

• Definition: Demand is relatively inelastic when the percentage change in quantity demanded is less than the percentage change in price. Consumers are not very responsive to price changes.
• Graphical Representation: The demand curve is steeply sloped (closer to vertical).
• Example: Necessities like salt, medicine, or electricity.
• Implication: A price increase leads to a small decrease in demand, increasing total revenue.

Numerical Example:

• Initial Price (P₁) = Rs. 20, Initial Quantity (Q₁) = 100 units
• New Price (P₂) = Rs. 25, New Quantity (Q₂) = 90 units

$$E_d=\frac{\frac{90-100}{100}}{\frac{25-20}{20}}=\frac{-0.1}{0.25}=-0.4(\text{Inelastic, }|E_d|<1)$$

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5. Perfectly Inelastic Demand (E_d = 0)

• Definition: Demand is perfectly inelastic when quantity demanded does not change at all despite any change in price. Consumers are completely unresponsive to price changes.
• Graphical Representation: The demand curve is a vertical line parallel to the y-axis.
• Example: Life-saving drugs (e.g., insulin for diabetics), addictive goods (e.g., cigarettes for heavy smokers).
• Implication: Firms can increase price without losing any customers.

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Factors Determining Price Elasticity of Demand

While the question does not ask for factors, it is useful to briefly mention them for completeness:

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Practical Implications of Price Elasticity

Understanding PED helps businesses and policymakers in:

• Pricing Strategies: Firms with inelastic demand can increase prices to boost revenue.
• Taxation Policies: Governments prefer taxing inelastic goods (e.g., tobacco) to maximize revenue.
• Advertising and Promotion: Elastic goods require more aggressive marketing to maintain sales.
• Forecasting Demand: Helps predict how consumers will react to price changes.

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Conclusion

Price elasticity of demand is a fundamental concept in economics that explains how consumers adjust their purchasing behavior in response to price changes. The five types—perfectly elastic, relatively elastic, unitary elastic, relatively inelastic, and perfectly inelastic—provide a framework for analyzing market behavior. Businesses and governments use this concept to make informed decisions on pricing, taxation, and resource allocation.