Price elasticity of demand and supply (VCE Economics Unit 3)
“The concept of price elasticity of demand and price elasticity of supply, the factors that affect each, and the relevance of elasticity to the operation of markets and to the effect of government intervention”
Price elasticity of demand measures how responsive quantity demanded is to price, and price elasticity of supply measures the same for quantity supplied. Demand is more elastic with more substitutes, for luxuries, for big-ticket items and over longer periods; supply is more elastic with spare capacity and over longer periods. Elasticity decides who bears an indirect tax: with inelastic demand, consumers pay most of it, which is why tobacco and fuel excises raise large revenue.
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What this dot point is asking
VCAA wants you to define price elasticity of demand and price elasticity of supply, explain the factors that determine each, and apply elasticity to how markets work and how government intervention (especially indirect taxes and subsidies) plays out. Expect short-response calculation and explanation questions plus extended responses linking elasticity to tax incidence.
The answer
Price elasticity of demand defined
Price elasticity of demand (PED) measures the responsiveness of quantity demanded to a change in the price of the good.
PED is normally negative (price and quantity move in opposite directions), so VCE convention uses the absolute value.
- Elastic (PED greater than 1): quantity is very responsive. A small price rise causes a large fall in quantity.
- Inelastic (PED less than 1): quantity is not very responsive. A price rise causes only a small fall in quantity.
- Unit elastic (PED equal to 1): the percentage changes are equal.
Determinants of price elasticity of demand
- Availability and closeness of substitutes. The single most important factor. More close substitutes makes demand more elastic, because buyers switch away when the price rises. One brand of petrol station is elastic; petrol as a whole is inelastic.
- Degree of necessity. Necessities (basic food, electricity, prescription medicine) have inelastic demand. Luxuries (restaurant meals, overseas travel) are elastic.
- Proportion of income spent. Goods that absorb a large share of income (a new car, a house) tend to be elastic; low-cost items (salt, matches) are inelastic.
- Time period. Demand is more elastic over a longer time horizon, because consumers can change habits, find substitutes, and replace equipment. Petrol demand is very inelastic this week but more elastic over several years as people buy more fuel-efficient cars.
- Addictiveness or habit. Addictive and habit-forming goods (tobacco, alcohol, caffeine) have inelastic demand.
Price elasticity of supply defined
Price elasticity of supply (PES) measures the responsiveness of quantity supplied to a change in price.
Determinants of price elasticity of supply
- Spare capacity. If firms have idle plant and labour, they can expand output quickly when price rises, so supply is elastic.
- Availability of inputs and stock. Easy access to extra inputs, and the ability to hold inventories, makes supply more elastic.
- Time period. The decisive factor. In the very short run, supply is often near-vertical (inelastic); over the long run, firms can build capacity and new firms can enter, so supply becomes more elastic.
- Ease of factor mobility. If resources can be shifted into the industry easily, supply is more elastic.
- Production lags. Agricultural and resource supply is inelastic in the short run because crops take a season to grow and mines take years to develop.
Elasticity and total revenue
For a price change, the effect on a firm's total revenue (price multiplied by quantity) depends on PED:
- Elastic demand: a price cut raises total revenue (the quantity gain outweighs the lower price).
- Inelastic demand: a price rise raises total revenue (the small quantity loss is outweighed by the higher price).
This is why firms with market power over goods with inelastic demand can raise revenue by raising prices, and why a bumper harvest (large supply rise) can lower farmers' total revenue when demand for food is inelastic.
Elasticity and government intervention
Tax incidence. When the government applies an indirect tax, the share borne by consumers versus producers depends on relative elasticities.
- Inelastic demand (relative to supply): consumers bear most of the tax. They keep buying despite the higher price, so producers pass the tax through. Revenue collected is high and the fall in quantity is small.
- Elastic demand: producers bear most of the tax. A higher price would cut quantity sharply, so firms absorb much of the tax. Revenue collected is lower and quantity falls more.
This is why "sin taxes" target inelastic goods: tobacco excise raises large revenue and the burden falls mainly on smokers, while still discouraging consumption at the margin.
Subsidies work in reverse: a subsidy on a good with inelastic demand mostly lowers the price paid by consumers; on an elastic good, more of the benefit shows up as higher quantity.
Price controls. The effect of a minimum or maximum price depends on elasticity. A minimum wage causes more unemployment where labour demand is elastic; a price ceiling on rent causes larger shortages where supply is inelastic.
- Forgetting the absolute value
- PED is mathematically negative. VCE uses the absolute value to classify elastic versus inelastic, so a PED of -2 is "elastic" (|-2| > 1).
- Confusing a movement along the curve with the elasticity of the curve
- Elasticity describes how responsive quantity is to a price change; it is a property measured at a point or over a range, not a shift.
- Saying tax is always passed to consumers
- Pass-through depends on relative elasticities. With elastic demand, producers absorb most of the tax.
- Treating all of agriculture or housing as one elasticity
- Short-run supply is usually inelastic; long-run supply is more elastic. Always specify the time period.
Examples in context
- Example 1. Tobacco excise
- Demand for cigarettes is highly inelastic (addiction, few substitutes), with PED estimates around 0.4 in absolute value. When the government raises tobacco excise, the retail price rises, quantity falls only modestly, and consumers bear most of the tax. This produces large excise revenue and a modest public-health reduction in smoking. The inelasticity is exactly why this good is targeted.
- Example 2. Petrol in the short and long run
- A spike in global oil prices raises pump prices, but motorists cannot quickly change their commute, so short-run demand is very inelastic and quantity barely falls. Over several years, households buy more fuel-efficient or electric vehicles and shift commuting patterns, so long-run demand is more elastic. The same good has different elasticities over different horizons.
- Example 3. Australian housing supply
- The dwelling stock is essentially fixed in the short run, so supply is highly inelastic. When net overseas migration surged through 2023-24, the demand shift right pushed rents and prices up sharply rather than expanding quantity. Only over a multi-year horizon, as construction responds, does supply become more elastic. Check current ABS and CoreLogic releases for the latest rent and dwelling figures.
Try this
Q1. Define price elasticity of demand and state the formula. [2 marks]
- Cue. Responsiveness of quantity demanded to a change in price; PED = (% change in quantity demanded) / (% change in price).
Q2. A 10 percent rise in the price of a good causes quantity demanded to fall by 4 percent. Calculate the PED and state whether demand is elastic or inelastic. [2 marks]
- Cue. PED = 4% / 10% = 0.4. Less than 1 in absolute value, so demand is inelastic.
Q3. Explain, using the concept of elasticity, why an indirect tax on tobacco raises large government revenue while a similar tax on a good with many substitutes would not. [4 marks]
- Cue. Tobacco demand is inelastic, so quantity falls little when price rises and consumers bear most of the tax, giving high revenue. A good with many substitutes has elastic demand, so a tax causes a large fall in quantity, producers absorb more of the tax, and revenue is lower.
Exam-style questions
Questions in the style of VCAA exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
Practice6 marksExplain the factors that influence the price elasticity of demand for a good, and discuss why this matters when the government places an indirect tax on that good.Show worked answer →
A 6 mark response needs the definition, at least three determinants, and the tax-incidence link.
Definition. Price elasticity of demand (PED) measures the responsiveness of quantity demanded to a change in price, calculated as the percentage change in quantity demanded divided by the percentage change in price.
Determinants.
- Availability of substitutes. More close substitutes makes demand more elastic, because buyers can switch away when price rises.
- Degree of necessity. Necessities (insulin, basic food) have inelastic demand; luxuries (overseas holidays) are elastic.
- Proportion of income. Goods that take a large share of income (a car) are more elastic than small-share goods (salt).
- Time. Demand is more elastic over a longer period as consumers adjust habits and find substitutes.
- Addictiveness. Addictive goods (tobacco) tend to be inelastic.
Tax incidence link. When demand is inelastic, consumers keep buying even as price rises, so producers can pass most of an indirect tax on to consumers as a higher price. The consumer bears most of the tax burden and the government raises substantial revenue. This is why tobacco excise (inelastic demand) raises large revenue and falls mainly on smokers, while a tax on a good with elastic demand would cut quantity sharply and be borne more by producers.
Markers reward (1) a correct PED definition, (2) at least three determinants, (3) the explicit incidence reasoning linking inelastic demand to consumer-borne tax.