What does price elasticity of demand measure, and what is the formula?

Price elasticity of demand measures how responsive the quantity demanded of a good is to a change in its own price. The formula is the percentage change in quantity demanded divided by the percentage change in price. Each percentage change is worked out as the change divided by the original value, multiplied by 100. The answer is a pure number with no units, because pounds and units of output cancel out, which is what makes elasticity values comparable between very different markets.

Why is elasticity measured using percentage changes rather than the raw change in pounds and units?

Raw changes depend on the units chosen and on the size of the market. A fall of 10p means something very different on a 40p newspaper than on a £400 flight, and a rise of 500 units means little unless you know whether sales were 1,000 or 1,000,000. Converting both changes into percentages of their original values strips out the units and the scale, so a price elasticity of demand of -2.00 means the same degree of responsiveness in every market it is calculated for.

A regional bus operator cuts a single fare from £10.00 to £9.00 and weekly journeys on that route rise from 400 to 480. Calculate the price elasticity of demand and interpret both its size and its sign.

Percentage change in price: the change is -£1.00, so -1.00 divided by 10.00, multiplied by 100, gives -10%. Percentage change in quantity: the change is +80 journeys, so 80 divided by 400, multiplied by 100, gives +20%. Price elasticity of demand is +20 divided by -10, which is -2.00. The sign is negative, which is normal: price and quantity moved in opposite directions. The modulus of 2.00 is greater than 1, so demand on this route is price elastic - quantity demanded is proportionately twice as responsive as the price change that caused it.

A café raises the price of a coffee from £2.00 to £2.40 and weekly sales fall from 1,000 to 900 cups. Calculate the price elasticity of demand and say what the value means.

Percentage change in price: +£0.40 divided by 2.00, multiplied by 100, gives +20%. Percentage change in quantity: -100 divided by 1,000, multiplied by 100, gives -10%. Price elasticity of demand is -10 divided by +20, which is -0.50. The negative sign shows the usual inverse relationship. The modulus of 0.50 lies between 0 and 1, so demand is price inelastic: customers cut back proportionately less than the price rose, meaning quantity demanded is relatively unresponsive to price on this product.

A supermarket raises the price of an own-label cereal from £1.20 to £1.50 and weekly sales fall from 2,000 to 1,400 boxes. Calculate the price elasticity of demand.

Percentage change in price: +£0.30 divided by 1.20, multiplied by 100, gives +25%. Percentage change in quantity: -600 divided by 2,000, multiplied by 100, gives -30%. Price elasticity of demand is -30 divided by +25, which is -1.20. The value is negative and its modulus of 1.20 exceeds 1, so demand for this cereal is price elastic. Shoppers found close alternatives on the same shelf and switched away proportionately more than the price rose.

An online retailer cuts the price of a set of headphones from £6.00 to £4.80 and monthly sales rise from 250 to 350 units. Calculate the price elasticity of demand and state whether demand is elastic or inelastic.

Percentage change in price: -£1.20 divided by 6.00, multiplied by 100, gives -20%. Percentage change in quantity: +100 divided by 250, multiplied by 100, gives +40%. Price elasticity of demand is +40 divided by -20, which is -2.00. Demand is price elastic, because the modulus of 2.00 is greater than 1. The negative sign simply confirms that quantity demanded rose as price fell, which is the normal direction for a demand relationship.

CCEA AS-Level Economics 4410

Key Economic Concepts

Topic overview The four factors of production Positive statements and normative judgements Economic agents and what they are trying to achieve Capital goods and consumption goods Product markets and factor markets

The Basic Economic Problem of Scarcity and Choice

Topic overview Scarcity, choice and opportunity cost Drawing and reading the production possibility frontier Using a PPF to show choice, opportunity cost, efficiency and growth Why an economy operates inside its frontier Specialisation and the division of labour Free market, planned and mixed economies

Demand and Supply in Product Markets

Topic overview What determines demand and what determines supply Movements along a curve versus shifts of a curve Why the demand curve slopes downwards Why the supply curve slopes upwards: marginal cost and the profit incentive Consumer surplus and producer surplus When consumers do not behave rationally

Markets and Equilibrium

Topic overview Market equilibrium and how markets clear How shifts in demand and supply change the equilibrium Price signals, incentives, rationing and the role of profit Joint, composite and derived demand and joint supply Tracing effects between interrelated markets Community surplus and allocative efficiency Demand and supply in housing, energy and commodity markets Indirect taxes and subsidies: impact and incidence

Elasticity of Demand and Supply

Topic overview Price elasticity of demand: measuring and interpreting Income and cross elasticity: normal, inferior, substitutes and complements Price elasticity of supply What determines the value of an elasticity Elasticity and total revenue How useful is elasticity for firms and government?

Factor Markets: Labour

Topic overview How a competitive labour market sets the wage Elasticity of labour demand and labour supply Wage differentials and why they persist Economic rent and transfer earnings Flexibility: trade unions, welfare and migration Minimum wages and government intervention in the labour market

Market Failures and Imperfections

Topic overview Market equilibrium, the social optimum and the meaning of market failure Externalities: private, external and social costs and benefits Community surplus and the externality diagrams Calculating and interpreting welfare loss Public goods, quasi-public goods and the free rider problem The consequences of missing markets for public goods Merit goods and demerit goods Information gaps and asymmetric information The consequences of merit goods, demerit goods and information failure Market power and other market imperfections Income and wealth inequality Absolute and relative poverty

Government Intervention in Markets

Topic overview Why governments step into markets Indirect taxes Subsidies, and choosing between taxes and subsidies Maximum and minimum prices State provision Regulation Information provision Tradeable pollution permits Government failure

The Circular Flow of Income

Topic overview Households, firms and the two-way flow Injections and withdrawals in an open economy with government Equilibrium and change in the circular flow

Measuring National Income

Topic overview Three routes to the same total: income, expenditure and output GDP as a measure of welfare and its limitations Domestic or national? GDP and GNP compared Nominal and real values: correcting for price changes Total and per capita measures

Aggregate Demand

Topic overview The four components of aggregate demand Why the aggregate demand curve slopes downwards Movements along and shifts in aggregate demand Factors that shift aggregate demand Investment: gross, net and fixed capital

Aggregate Supply

Topic overview Why short-run aggregate supply slopes upwards Factors that shift short-run aggregate supply Movements along and shifts in aggregate supply From the short run to the long run What determines long-run aggregate supply Keynesian and neoclassical views of long-run aggregate supply

Macroeconomic Equilibrium

Topic overview How aggregate demand and aggregate supply determine equilibrium Applying AD-AS analysis to growth and unemployment Applying AD-AS analysis to inflation

Macroeconomic Objectives

Topic overview Why governments target inflation, unemployment, the external balance and growth Objectives beyond the main four: the environment and the distribution of income and wealth Picturing inequality: the Lorenz curve and the Gini coefficient Where the objectives collide: the main policy conflicts Judging the trade-offs: how sharp is a conflict?

Inflation

Topic overview Inflation, deflation and disinflation: what the words actually mean Measuring the rate: the CPI and the RPI Working with index numbers Building a price index: the basket and the significance of weights Demand-pull and cost-push inflation The costs and consequences of inflation and deflation The policy response to inflation

Unemployment

Topic overview The claimant count and the ILO measure of unemployment Calculating and interpreting unemployment statistics Unemployment and economic inactivity: a distinction that changes the numbers The types of unemployment and what distinguishes them The causes of unemployment and of economic inactivity The costs and consequences of unemployment and inactivity Policies for unemployment and intervention in the labour market

Economic Growth

Topic overview Actual and potential growth on a production possibility frontier Measuring economic growth The economic cycle and output gaps The causes of economic growth Benefits, costs and the sustainability of growth Policies to promote economic growth using AD–AS analysis

Fiscal Policy and Its Effects

Topic overview What fiscal policy is and how it works Government spending and taxation: the main categories Direct and indirect taxation Fiscal policy in the AD-AS model Evaluating the impact of fiscal policy on output, employment, prices and agents

Monetary Policy

Topic overview The nature of monetary policy and the interest rate instrument The transmission mechanism from interest rates to aggregate demand Monetary policy in the AD-AS model Evaluating the impact of monetary policy on output, employment, prices and agents

Supply-Side Policies

Topic overview The nature of supply-side policy and tax cuts Deregulation and evaluating market-based supply-side policy Competition and innovation as supply-side policy Infrastructure as supply-side policy Labour market reform Education, training and the skills of the workforce Labour productivity: determinants and significance Supply-side policies in the AD-AS model Evaluating the impact of supply-side policies

Exchange Rates and the National Economy

Topic overview What an exchange rate is and how it is measured Exchange rate changes in the AD-AS model Holding the exchange rate above or below the market clearing level Why a government might have an exchange rate policy Evaluating the impact of exchange rate changes on output, employment, prices and agents

Quantitative Skills in Economics

Topic overview Ratios, shares and proportions in economic data Percentages and percentage changes in economic data Averages, medians and quantiles Index numbers, weighting and rebasing Converting money values to real values Cost, revenue and profit Elasticity: calculating the number and reading its meaning Choosing and reading economic charts and diagrams Interpreting economic data critically

Elasticity of Demand and Supply

6 subtopics
12 things to know
Unit AS 1

What Elasticity of Demand and Supply covers

Elasticity of demand and supply is examined in Unit AS 1, Markets and Market Failure. It covers price elasticity of demand: measuring and interpreting, income and cross elasticity: normal, inferior, substitutes and complements, price elasticity of supply, what determines the value of an elasticity, elasticity and total revenue and how useful is elasticity for firms and government?.

Where it is assessed

Unit AS 1

Markets and Market Failure, written examination, 20% of A level.

Check the CCEA specification ↗

The 6 subtopics

Each one has its own page. CCEA AS Economics students sit this topic in the first year.

What you need to know

Answer each one before you reveal it.

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Key term

What does price elasticity of demand measure, and why is it measured in percentages?

Key term

Set out the full interpretation of income elasticity of demand values, from strongly negative to strongly positive.

Key term

Set out the interpretation of price elasticity of supply values from 0 upwards.

Key term

Why does the price elasticity of supply of a good determine how quickly a shortage is cleared?

Key term

Why does the number and closeness of available substitutes have such a strong effect on price elasticity of demand?

Key term

Why is demand for a habit-forming or addictive product typically price inelastic?

Key term

Explain how the time period available to producers affects price elasticity of supply.

Numbers

A rail operator raises a season ticket from £25.00 to £27.50 and monthly sales fall from 4,000 to 3,400. Calculate the change in total revenue.

Key term

A firm cuts its price, sees total revenue rise, and concludes it should keep cutting. What is wrong with that reasoning?

Key term

Evaluate the usefulness of price elasticity of demand to a government deciding which goods to place an indirect tax on.

Key term

How far is it true that a government can always raise more revenue by increasing the duty on a habit-forming product?

Key term

Evaluate the claim that because elasticity estimates drift over time they are of little practical use.

Take Elasticity of Demand and Supply further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

A positive cross price elasticity vs A negative cross price elasticity
A positive cross price elasticity: the goods are substitutes: when the price of one rises, buyers move to the other. A negative cross price elasticity: it means complements: when the price of one rises, demand for the other falls.

Questions from this topic

Each one with the model answer underneath.

1
What does price elasticity of demand measure, and what is the formula?
Model answer
Price elasticity of demand measures how responsive the quantity demanded of a good is to a change in its own price. The formula is the percentage change in quantity demanded divided by the percentage change in price. Each percentage change is worked out as the change divided by the original value, multiplied by 100. The answer is a pure number with no units, because pounds and units of output cancel out, which is what makes elasticity values comparable between very different markets.
2
Why is elasticity measured using percentage changes rather than the raw change in pounds and units?
Model answer
Raw changes depend on the units chosen and on the size of the market. A fall of 10p means something very different on a 40p newspaper than on a £400 flight, and a rise of 500 units means little unless you know whether sales were 1,000 or 1,000,000. Converting both changes into percentages of their original values strips out the units and the scale, so a price elasticity of demand of -2.00 means the same degree of responsiveness in every market it is calculated for.
3
A regional bus operator cuts a single fare from £10.00 to £9.00 and weekly journeys on that route rise from 400 to 480. Calculate the price elasticity of demand and interpret both its size and its sign.
Model answer
Percentage change in price: the change is -£1.00, so -1.00 divided by 10.00, multiplied by 100, gives -10%. Percentage change in quantity: the change is +80 journeys, so 80 divided by 400, multiplied by 100, gives +20%. Price elasticity of demand is +20 divided by -10, which is -2.00. The sign is negative, which is normal: price and quantity moved in opposite directions. The modulus of 2.00 is greater than 1, so demand on this route is price elastic - quantity demanded is proportionately twice as responsive as the price change that caused it.
4
A café raises the price of a coffee from £2.00 to £2.40 and weekly sales fall from 1,000 to 900 cups. Calculate the price elasticity of demand and say what the value means.
Model answer
Percentage change in price: +£0.40 divided by 2.00, multiplied by 100, gives +20%. Percentage change in quantity: -100 divided by 1,000, multiplied by 100, gives -10%. Price elasticity of demand is -10 divided by +20, which is -0.50. The negative sign shows the usual inverse relationship. The modulus of 0.50 lies between 0 and 1, so demand is price inelastic: customers cut back proportionately less than the price rose, meaning quantity demanded is relatively unresponsive to price on this product.
5
A supermarket raises the price of an own-label cereal from £1.20 to £1.50 and weekly sales fall from 2,000 to 1,400 boxes. Calculate the price elasticity of demand.
Model answer
Percentage change in price: +£0.30 divided by 1.20, multiplied by 100, gives +25%. Percentage change in quantity: -600 divided by 2,000, multiplied by 100, gives -30%. Price elasticity of demand is -30 divided by +25, which is -1.20. The value is negative and its modulus of 1.20 exceeds 1, so demand for this cereal is price elastic. Shoppers found close alternatives on the same shelf and switched away proportionately more than the price rose.
6
An online retailer cuts the price of a set of headphones from £6.00 to £4.80 and monthly sales rise from 250 to 350 units. Calculate the price elasticity of demand and state whether demand is elastic or inelastic.
Model answer
Percentage change in price: -£1.20 divided by 6.00, multiplied by 100, gives -20%. Percentage change in quantity: +100 divided by 250, multiplied by 100, gives +40%. Price elasticity of demand is +40 divided by -20, which is -2.00. Demand is price elastic, because the modulus of 2.00 is greater than 1. The negative sign simply confirms that quantity demanded rose as price fell, which is the normal direction for a demand relationship.

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Key Economic Concepts

The Basic Economic Problem of Scarcity and Choice

Demand and Supply in Product Markets

Markets and Equilibrium

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Elasticity of Demand and Supply revision questions

Is Elasticity of Demand and Supply examined at AS in CCEA Economics?: Yes. It sits in Unit AS 1, which you take in the first year, so it is on the AS paper as well as counting towards the full A level.
What does Elasticity of Demand and Supply cover in CCEA AS-Level Economics?: 6 subtopics: price elasticity of demand: measuring and interpreting, income and cross elasticity: normal, inferior, substitutes and complements, price elasticity of supply, what determines the value of an elasticity, elasticity and total revenue and how useful is elasticity for firms and government?. Each one has its own page with questions and model answers.
How is Elasticity of Demand and Supply organised?: By the CCEA 4410 specification, subtopic by subtopic, so it matches the order you are taught it in.

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