What you'll learn
Price elasticity measures how responsive quantity demanded or supplied is to changes in price. This concept is fundamental to understanding consumer behaviour, producer decisions, and government policy effectiveness in Caribbean economies. You will learn to calculate, interpret, and apply both price elasticity of demand (PED) and price elasticity of supply (PES) to real-world scenarios that appear regularly in CXC CSEC Economics examinations.
Key terms and definitions
Price Elasticity of Demand (PED) — the responsiveness of quantity demanded to a change in price, measured as the percentage change in quantity demanded divided by the percentage change in price.
Price Elasticity of Supply (PES) — the responsiveness of quantity supplied to a change in price, measured as the percentage change in quantity supplied divided by the percentage change in price.
Elastic demand — when the percentage change in quantity demanded is greater than the percentage change in price (PED > 1), meaning consumers are highly responsive to price changes.
Inelastic demand — when the percentage change in quantity demanded is less than the percentage change in price (PED < 1), meaning consumers are relatively unresponsive to price changes.
Unitary elasticity — when the percentage change in quantity demanded or supplied equals the percentage change in price (elasticity = 1).
Total revenue — the total income received by producers from selling goods or services, calculated as price multiplied by quantity sold.
Necessities — goods that consumers need regardless of price changes, typically demonstrating inelastic demand (e.g., rice, flour, medication).
Luxuries — goods that consumers can easily do without, typically demonstrating elastic demand (e.g., jewellery, restaurant meals, tourism packages).
Core concepts
Calculating price elasticity of demand
The formula for PED is:
PED = (% change in quantity demanded) ÷ (% change in price)
To calculate percentage change: % change = (New value - Original value) ÷ Original value × 100
PED values are normally negative because of the inverse relationship between price and quantity demanded (the law of demand). However, economists often ignore the negative sign and focus on the absolute value when classifying elasticity.
Example calculation:
- Original price of dasheen: $4 per pound
- New price: $5 per pound
- Original quantity demanded: 1,000 pounds
- New quantity demanded: 700 pounds
% change in price = (5 - 4) ÷ 4 × 100 = 25% % change in quantity demanded = (700 - 1,000) ÷ 1,000 × 100 = -30%
PED = -30% ÷ 25% = -1.2 (or 1.2 in absolute terms)
This shows elastic demand since the value is greater than 1.
Interpreting PED values
Perfectly inelastic demand (PED = 0) Quantity demanded does not change at all when price changes. This is rare but can occur with life-saving medications or essential utilities where consumers have no alternatives.
Inelastic demand (0 < PED < 1) Quantity demanded changes by a smaller percentage than the price change. Common for:
- Necessities (bread, rice, cooking oil)
- Products with few substitutes (prescription drugs, electricity)
- Habitual purchases (cigarettes, coffee)
- Items that represent a small proportion of income (salt, matches)
Unitary elastic demand (PED = 1) Quantity demanded changes by exactly the same percentage as price. Total revenue remains constant when price changes.
Elastic demand (PED > 1) Quantity demanded changes by a larger percentage than the price change. Common for:
- Luxury goods (designer clothing, fine dining)
- Products with many substitutes (different brands of soft drinks)
- Non-essential items (entertainment, tourism services)
- Items purchased infrequently (furniture, appliances)
Perfectly elastic demand (PED = ∞) Any price increase causes quantity demanded to fall to zero. Occurs in perfectly competitive markets where products are identical and consumers will not pay even slightly more than the market price.
Factors affecting price elasticity of demand
Availability of substitutes The more substitutes available, the more elastic the demand. If the price of Jamaican Blue Mountain coffee increases significantly, consumers can switch to Colombian or Costa Rican coffee. However, if electricity prices increase, consumers have few alternatives, making demand inelastic.
Necessity versus luxury Necessities like ground provisions (yams, cassava, sweet potatoes) have inelastic demand because Caribbean households need these staples regardless of price. Luxury items like cruise holidays have elastic demand because they are easily postponed or cancelled.
Proportion of income spent Goods that take up a large proportion of income (cars, overseas university tuition) have more elastic demand than items taking a small proportion (bus fare, newspaper).
Time period Demand becomes more elastic over time as consumers find alternatives. When petrol prices first increase, demand may be inelastic, but over months consumers might use public transport, carpool, or buy more fuel-efficient vehicles.
Habit and brand loyalty Products with strong brand loyalty or habitual consumption (certain brands of hot sauce, specific types of rum) tend to have more inelastic demand.
Price elasticity of supply
The formula for PES is:
PES = (% change in quantity supplied) ÷ (% change in price)
Unlike PED, PES is always positive because price and quantity supplied move in the same direction according to the law of supply.
Perfectly inelastic supply (PES = 0) Quantity supplied cannot change regardless of price. Examples include:
- Caribbean beachfront land (fixed quantity)
- Original artwork by deceased artists
- Agricultural products at harvest time (already grown)
Inelastic supply (0 < PES < 1) Quantity supplied changes by a smaller percentage than price. Common for:
- Agricultural products in the short run (crops take time to grow)
- Goods requiring specialized resources (banana production requires specific climate)
- Products with long production times (livestock rearing, tree crops like nutmeg)
Unitary elastic supply (PES = 1) Quantity supplied changes by the same percentage as price.
Elastic supply (PES > 1) Quantity supplied changes by a larger percentage than price. Common for:
- Manufactured goods with spare capacity
- Services (hairdressing, tutoring)
- Products with readily available inputs
Perfectly elastic supply (PES = ∞) Suppliers will supply any amount at the current price but nothing at a lower price. Theoretical concept often used in perfect competition models.
Factors affecting price elasticity of supply
Time period
- Momentary period: Supply is perfectly inelastic (e.g., fresh fish already caught)
- Short run: Some factors of production are fixed, supply is relatively inelastic
- Long run: All factors can be adjusted, supply becomes more elastic
Availability of factors of production If labour, raw materials, and capital are readily available, supply is more elastic. Shortages make supply inelastic.
Spare capacity Firms operating below full capacity can increase supply more easily, making supply more elastic. Hotels in Barbados during low season have elastic supply; during peak season, supply is inelastic.
Mobility of factors of production If workers can easily move between industries and machinery can be adapted, supply is more elastic. Specialized equipment for processing sugar cane cannot easily be used for other purposes, making sugar supply relatively inelastic.
Ability to store goods Products that can be stored (canned goods, packaged snacks) have more elastic supply than perishables (ripe mangoes, fresh fish).
Relationship between PED and total revenue
Understanding this relationship is crucial for business pricing decisions and tax policy analysis.
When demand is elastic (PED > 1):
- Price decrease → Total revenue increases
- Price increase → Total revenue decreases
Example: If hotels in Trinidad reduce room rates by 10% and bookings increase by 20%, total revenue rises because the percentage increase in quantity is greater than the percentage decrease in price.
When demand is inelastic (PED < 1):
- Price decrease → Total revenue decreases
- Price increase → Total revenue increases
Example: If bus fares in Kingston increase by 15% and passenger numbers only fall by 5%, total revenue for transport companies increases.
When demand is unitary elastic (PED = 1):
- Price changes do not affect total revenue
- Percentage changes in price and quantity offset each other exactly
Applications of price elasticity
Government tax policy Governments in Caribbean countries prefer taxing goods with inelastic demand (cigarettes, alcohol, petrol) because:
- Revenue collected is substantial even if prices increase significantly
- Quantity demanded falls only slightly, so tax revenue remains high
- The tax burden falls mainly on consumers
Business pricing strategies
- Firms selling products with elastic demand should lower prices to increase total revenue
- Firms selling products with inelastic demand can increase prices to boost revenue
- Airlines use dynamic pricing, charging higher prices when demand is inelastic (holiday periods, last-minute bookings)
Agricultural policy Understanding PES helps explain why agricultural prices fluctuate. When prices rise, farmers cannot immediately increase supply (inelastic in short run), so prices remain high. Good harvests increase supply significantly, but inelastic demand means prices must fall sharply to clear the market.
Minimum wage policy If labour supply is inelastic, minimum wage increases have less impact on employment. If labour demand is elastic, employment may fall significantly when wages increase.
Worked examples
Example 1: Calculating and interpreting PED (6 marks)
Question: The price of plantains at Coronation Market increased from $80 to $100 per dozen. As a result, the quantity demanded fell from 500 dozen to 400 dozen per week.
(a) Calculate the price elasticity of demand for plantains. (4 marks) (b) State whether demand is elastic or inelastic and explain what this means. (2 marks)
Answer:
(a) % change in price = (100 - 80) ÷ 80 × 100 = 25% ✓
% change in quantity demanded = (400 - 500) ÷ 500 × 100 = -20% ✓
PED = -20% ÷ 25% = -0.8 ✓
The PED is 0.8 in absolute terms ✓
(b) Demand is inelastic ✓ because the PED value is less than 1. This means the percentage change in quantity demanded is smaller than the percentage change in price / consumers are relatively unresponsive to price changes. ✓
Example 2: PED and total revenue (5 marks)
Question: A tour operator in Grenada currently charges $120 per person for a day tour and sells 200 tours weekly. The company calculates that demand for its tours has a PED of 1.5.
(a) Calculate current total revenue. (1 mark) (b) If the company reduces its price to $100, explain what will happen to total revenue. (4 marks)
Answer:
(a) Total revenue = $120 × 200 = $24,000 ✓
(b) Demand is elastic (PED > 1) ✓, which means when price falls, total revenue will increase ✓. This is because the percentage increase in quantity demanded will be greater than the percentage decrease in price ✓. More people will book tours at the lower price, and the increase in bookings will more than compensate for the lower price per tour. ✓
Example 3: Factors affecting elasticity (4 marks)
Question: Explain TWO reasons why demand for prescription medicine is likely to be price inelastic.
Answer:
Prescription medicine is a necessity ✓ as people need it to treat illness and maintain health regardless of price changes ✓.
There are few or no substitutes available ✓ because patients must take the specific medication prescribed by their doctor and cannot easily switch to alternatives ✓.
(Other acceptable answers: takes small proportion of income when seriously ill; addictive/habit-forming nature of some medications)
Common mistakes and how to avoid them
Forgetting to convert to percentages: Always calculate percentage changes, not absolute changes. If price increases from $2 to $3 and quantity falls from 100 to 80, don't calculate 1 ÷ 20. Calculate (50% ÷ -20%) = -2.5.
Confusing elastic with inelastic: Remember that elastic means responsive (bendable) and inelastic means unresponsive (rigid). Elastic demand has PED > 1, inelastic has PED < 1.
Misunderstanding the revenue relationship: Students often think higher prices always mean higher revenue. When demand is elastic, price increases reduce total revenue because quantity demanded falls proportionally more.
Ignoring the time factor: Always consider that elasticity changes over time. A product may have inelastic demand in the short run but elastic demand in the long run as consumers find alternatives.
Using wrong formula: PED uses quantity demanded (consumer response), while PES uses quantity supplied (producer response). Don't confuse them.
Not showing working: Even if your final answer is wrong, you can earn method marks by clearly showing percentage calculations and the elasticity formula.
Exam technique for "Price Elasticity"
"Calculate" questions: Show all working clearly. Write the formula, calculate each percentage change separately, then divide them. Use the correct formula: PED or PES. Typical allocation: 3-4 marks.
"Explain" questions: Define the term, apply the concept to the scenario, and give reasons. For example, "Explain why demand for rice is price inelastic" requires: definition of inelastic demand (1 mark), statement that rice is a necessity (1 mark), explanation that consumers need it regardless of price (1 mark). Usually 2-3 marks per explanation.
"State and explain factors": For questions asking about factors affecting elasticity, clearly separate each factor. Use Caribbean examples where appropriate to demonstrate application, not just memorization.
Linking to total revenue: Questions often ask you to use PED to explain business decisions or predict revenue changes. State the elasticity value, identify whether it's elastic/inelastic, then explain the impact on total revenue with clear reasoning.
Quick revision summary
Price elasticity of demand (PED) measures consumer responsiveness to price changes: elastic demand (PED > 1) means quantity demanded changes proportionally more than price, while inelastic demand (PED < 1) means relatively unresponsive consumers. Price elasticity of supply (PES) measures producer responsiveness. Key factors affecting PED include availability of substitutes, necessity versus luxury, proportion of income, and time period. When demand is elastic, price decreases increase total revenue; when inelastic, price increases raise revenue. Caribbean governments tax inelastic goods (alcohol, cigarettes) to maximize revenue. Calculate elasticity using percentage changes, not absolute values.