Microeconomics guide, Unit 2, step 11 of 28Previous step Next step

Step 11: Government Intervention in Markets

By the EconTutorials team. 11-minute read with 6 practice questions.

SyllabusAP Micro 2.8 · Cambridge 3.1–3.2 · IB 2.7

In 30 seconds

Governments use price ceilings, price floors, taxes, subsidies, regulation, nationalisation and competition policy to fix market failures or to help particular groups.
A price control only matters if it is binding: a ceiling must be below equilibrium (causing a shortage) and a floor above it (causing a surplus).
Who really pays a tax depends on elasticity, not on who hands the money over: $ \dfrac{\text{burden on buyers}}{\text{burden on sellers}} = \dfrac{PES}{PED} $. The less elastic side pays more.
Intervention can backfire. Government failure happens when policy leaves resources allocated worse than the market did.

Video lesson coming soonA short animated lesson for this step will appear here.

Price ceilings: when the government caps a price

Imagine your city bans charging more than $800 a month for student flats. Great news, if you can find one. At $800, far more students want flats than landlords offer, so you end up on a waiting list, paying a “fee” under the table, or in a flat nobody maintains.

That is a price ceiling: a legal maximum price. Governments use ceilings for rent control, energy price caps and caps on medicine prices.

Key termPrice ceiling: a legally imposed maximum price. It is binding only if it is set below the equilibrium price, and then it creates a shortage.

A ceiling set above equilibrium does nothing: the market price is already lower, and that price is legal. Once a ceiling binds, expect these effects:

Shortage: quantity demanded is greater than quantity supplied.
Non-price rationing: queues, waiting lists, favouritism or bribes decide who gets the good.
Black markets: illegal trading above the cap, such as rent-controlled flats sublet at market rents.
Lower quality: landlords cut back on maintenance.
Less supply in the long run: suppliers leave the market or stop investing.
Deadweight loss: trades that would have helped both buyer and seller no longer happen.

Worked example

In a city’s rental market, $ Q_d = 900 – 30P $ and $ Q_s = 100 + 50P $, where $ P $ is monthly rent in hundreds of dollars. The city caps rent at $ P = 8 $. Find the equilibrium, then the shortage.

Step 1$ 900 – 30P = 100 + 50P \Rightarrow 800 = 80P \Rightarrow P^* = 10 $, $ Q^* = 900 – 300 = 600 $

Step 2$ 8 < 10 $, so the ceiling binds. $ Q_d = 900 – 30(8) = 660 $; $ Q_s = 100 + 50(8) = 500 $

Step 3Shortage $ = 660 – 500 = 160 $ flats; flats actually rented $ = 500 $

Rent falls from $1,000 to $800, but only 500 flats are rented instead of 600, and 160 households miss out. The quantity traded is set by the short side of the market, here supply.

Berlin tried this in 2020 with a rent freeze on about 1.5 million older flats. Regulated rents fell by about 11% within a year, but rental listings in the regulated market fell by around 50% within nine months, and rents in the uncapped new-build segment rose faster than before. Germany’s Federal Constitutional Court struck the law down in April 2021. Existing tenants gained; newcomers and young people searching for a home lost out.

Price floors: when the government sets a minimum

A price floor is a legal minimum price. It is binding only if it is set above equilibrium. At the higher price, sellers want to sell more than buyers want to buy, so there is a surplus.

The two big examples are the minimum wage (Step 15), where the surplus is unemployment, and farm price supports. In the 1980s, the EU’s Common Agricultural Policy guaranteed to buy food at above-market prices. It ended up with “butter mountains” and “wine lakes” of unsold produce that cost billions to store and dispose of. Later reforms switched to direct income support for farmers, which distorts the market less.

Common mistakeAnalysing a price control without checking whether it binds. If bread’s equilibrium price is $2 and the government sets a maximum of $3, nothing happens: no shortage and no deadweight loss. Examiners include non-binding controls on purpose to catch this.

Taxes: who really pays?

From Step 9 you know that a per-unit tax raises the price buyers pay, lowers the price sellers receive, reduces the quantity traded, raises revenue and creates deadweight loss. The question now is: who bears the burden?

Key termTax incidence: how the burden of a tax is split between buyers and sellers. It depends on the elasticities of demand and supply, not on who is legally required to pay.

Smokers find it hard to quit, so cigarette demand is inelastic, and a cigarette tax mostly raises the price smokers pay. The side with fewer alternatives, the less elastic side, bears most of the tax.

\[ \frac{\text{Burden on buyers}}{\text{Burden on sellers}} = \frac{PES}{PED} \]

Use the size of PED (ignore the minus sign). The extreme cases: if $ PED = 0 $ (as for insulin), buyers bear the whole tax; if $ PES = 0 $ (as for land), sellers bear it all.

Worked example

A $2 tax is placed on each pack of cigarettes. Demand has $ PED = -0.4 $ and supply has $ PES = 2.0 $. How is the tax split?

Step 1Ratio $ = \dfrac{PES}{PED} = \dfrac{2.0}{0.4} = 5 $: buyers bear 5 parts for every 1 part sellers bear

Step 2Buyers: $ \tfrac{5}{6} \times 2 \approx \$1.67 $ per pack

Step 3Sellers: $ \tfrac{1}{6} \times 2 \approx \$0.33 $ per pack (check: $ 1.67 + 0.33 = 2 $)

Smokers pay about $1.67 more per pack, while tobacco firms receive only about 33 cents less. Cigarette taxes fall mainly on smokers.

Worked example

Before a $4 tax, a good sells at $12 and 1,000 units are traded. After the tax, buyers pay $15, sellers receive $11 and 850 units are traded. Find each side’s burden, the tax revenue and the deadweight loss.

Step 1Buyers: $ 15 – 12 = \$3 $; sellers: $ 12 – 11 = \$1 $ (check: $ 3 + 1 = 4 $)

Step 2Revenue $ = 4 \times 850 = \$3{,}400 $

Step 3$ DWL = \tfrac{1}{2} \times 4 \times (1{,}000 – 850) = \tfrac{1}{2} \times 4 \times 150 = \$300 $

Buyers bear three-quarters of the tax, so demand is less elastic than supply. The 150 lost trades cost society $300.

Exam tipIt makes no difference whether the law taxes buyers or sellers. Taxing sellers shifts supply up; taxing buyers shifts demand down. But the price buyers pay, the price sellers receive and the quantity traded all end up the same. Only elasticity decides the split.

Subsidies

A subsidy is a government payment that lowers the cost of producing or buying a good. It shifts supply down (or demand up) by the amount of the subsidy. Buyers pay less, sellers receive more and more is traded. Subsidies make sense when there is a positive externality (Step 16), such as vaccination, education, renewable energy or public transport. A subsidy equal to the external benefit per unit moves the market to the socially optimal quantity.

Subsidies have drawbacks too:

They cost taxpayers, and the taxes that fund them create deadweight loss elsewhere.
A subsidy bigger than the external benefit leads to overproduction.
Once introduced, they are hard to remove, because the people who benefit lobby hard to keep them. The IMF estimated global fossil-fuel subsidies at $7 trillion in 2022.
Protected industries may stop trying to become more efficient.

Regulation, nationalisation and competition policy

Tool	What it does	Strength	Weakness
Direct regulation	Sets rules: emission limits, safety standards, licensing	Certain and enforceable	Inflexible: treats all firms the same whatever their costs
Nationalisation	The state owns an industry, usually a natural monopoly (water, rail)	Can price at marginal cost and fund loss-making but valuable services	Weak pressure to keep costs down; risk of political meddling
Competition policy	Blocks harmful mergers, bans cartels, breaks up dominant firms	Prevents abuse of monopoly power	Cases are slow and complex

Examples of competition policy include the US Sherman Act (1890), the UK Competition and Markets Authority and the EU’s Digital Markets Act (2022) for large tech platforms.

Government failure

A market failure does not automatically mean the government should step in. You also have to show that intervention will make things better.

Key termGovernment failure: when government intervention leads to a less efficient allocation of resources than the market outcome it was meant to correct.

It has four main causes:

Information problems: governments rarely know the true external cost or the elasticities, so a Pigouvian tax set at the wrong level can make things worse.
Unintended consequences: EU biofuel mandates drove palm-oil deforestation in Indonesia and raised net emissions; rent controls shrink housing supply.
Regulatory capture and political incentives: a small group that benefits a lot lobbies harder than millions of taxpayers who each lose a little, which is how US ethanol subsidies survive.
Administrative costs: if monitoring and enforcement cost more than the efficiency gain, society ends up worse off.

Practise: 6 questions

Try each one on paper first, then check the worked answer.

EasyQ1. The equilibrium price of bread is $2. The government sets a maximum price of $3. What happens? Show worked answer

Nothing. The ceiling is above equilibrium, so it is not binding. The market still clears at $2, which is legal. There is no shortage and no deadweight loss.

EasyQ2. Supply of land is perfectly inelastic ($ PES = 0 $). Who bears a per-unit tax on land, and why? Show worked answer

Landowners (sellers) bear the entire tax.
Supply cannot fall in response to a lower net price, so landowners cannot escape the tax. The price buyers pay does not change. Using the formula, $ PES \div PED = 0 $, so buyers’ share is zero.

MediumQ3. In a rental market, $ Q_d = 1{,}200 – 20P $ and $ Q_s = 200 + 30P $ ($ P $ in hundreds of dollars). A rent ceiling of $ P = 15 $ is imposed. Find the equilibrium, the shortage and the number of apartments rented. Show worked answer

Equilibrium: $ 1{,}200 – 20P = 200 + 30P \Rightarrow 1{,}000 = 50P \Rightarrow P^* = 20 $ ($2,000), $ Q^* = 1{,}200 – 400 = 800 $.
$ 15 < 20 $, so the ceiling binds.
$ Q_d = 1{,}200 – 300 = 900 $; $ Q_s = 200 + 450 = 650 $.
Shortage $ = 900 – 650 = 250 $. Apartments rented $ = 650 $ (the short side, supply).

MediumQ4. A $3 tax is imposed. Before: $ P = \$20 $, $ Q = 500 $. After: buyers pay $22, sellers receive $19, $ Q = 440 $. Find each side’s burden, the revenue and the deadweight loss. Which side is less elastic? Show worked answer

Buyers: $ 22 – 20 = \$2 $. Sellers: $ 20 – 19 = \$1 $. Total $3 ✓.
Revenue $ = 3 \times 440 = \$1{,}320 $.
$ DWL = \tfrac{1}{2} \times 3 \times (500 – 440) = \tfrac{1}{2} \times 3 \times 60 = \$90 $.
Demand is less elastic, because buyers bear the larger share ($2 compared with $1).

MediumQ5. A $4,000 subsidy is paid on each electric car. Before: $ P = \$40{,}000 $, $ Q = 100{,}000 $. After: buyers pay $37,500, producers receive $41,500, $ Q = 130{,}000 $. Find each side’s gain and the total cost to taxpayers. Show worked answer

Buyers gain $ 40{,}000 – 37{,}500 = \$2{,}500 $ per car. Producers gain $ 41{,}500 – 40{,}000 = \$1{,}500 $ per car. Total $4,000 ✓ (buyers get 62.5%).
Cost $ = 4{,}000 \times 130{,}000 = \$520{,}000{,}000 $ ($520 million).

ExamQ6. Using the electric-car subsidy in Q5, suppose the external benefit of each car is $3,000. Is the subsidy too large, too small or about right? Explain. [3 marks] Show worked answer

Too large. The optimal subsidy equals the external benefit per unit, which is $3,000. [1]
A $4,000 subsidy pushes output beyond the socially optimal quantity, so some cars are produced whose social benefit is less than their social cost. This creates deadweight loss from overproduction. [1]
Evaluation: the external benefit may be understated if it leaves out air-quality or energy-security gains, or a temporary extra subsidy might be justified to help build charging networks. [1]

Check yourself

1. A price ceiling has no effect on a market if it is set:

The market already clears at a lower, legal price, so the ceiling does not bind.

2. The burden of a per-unit tax falls mainly on consumers when:

The less elastic side has fewer alternatives and bears more of the tax; legal incidence does not matter.

3. Which of these is an example of government failure?

The policy produced the opposite of its goal through an unintended consequence.

Your score: 0 out of 3

The short version

A binding price ceiling (below equilibrium) causes shortages, queues, black markets, lower quality and deadweight loss, as Berlin’s rent freeze showed.
A binding price floor (above equilibrium) causes surpluses, such as unemployment or EU butter mountains. Always check whether a control binds.
Tax incidence depends on elasticity: buyers’ burden divided by sellers’ burden equals $ PES \div PED $. It does not matter who legally pays.
Subsidies can fix positive externalities but cost taxpayers and are hard to remove. Regulation, nationalisation and competition policy each have trade-offs.
Government failure (information gaps, unintended consequences, capture, admin costs) means intervention must be well designed, not just well meant. The full chapter in Economics Made Simple has 15 exam-style questions with complete answers.

Step 11: Government Intervention in Markets

Price ceilings: when the government caps a price

Price floors: when the government sets a minimum

Taxes: who really pays?

Subsidies

Regulation, nationalisation and competition policy

Government failure

Practise: 6 questions

Check yourself

The short version

Further reading on EconTutorials

Contact Info

Quick Links

Success!