Definition
Market failure occurs when the free market allocates resources inefficiently, so society's welfare is not maximised. The market produces too much of some goods and too little of others.
The key idea is allocative efficiency: resources should be allocated so that the marginal social benefit equals the marginal social cost.
Why it matters in the exam
Market failure is one of the most examined topics in A-Level Economics. It appears in:
- definition questions
- diagram questions
- 20-mark essays on government intervention
- evaluation questions about whether policy works
If you can explain market failure clearly, you can answer a large share of the paper.
The main causes
| Cause | What it means |
|---|---|
| Externalities | Costs or benefits fall on third parties not involved in the transaction |
| Public goods | Goods that are non-excludable and non-rival, so markets underprovide them |
| Merit and demerit goods | Consumers underestimate benefits or underestimate harm |
| Monopoly power | A firm restricts output and raises price to increase profit |
| Information failure | Buyers or sellers do not have full or accurate information |
| Factor immobility | Resources cannot move quickly to where they are needed |
The diagram examiners expect
For an externality, draw:
- MPC — marginal private cost
- MSC — marginal social cost
- MPB = MSB — marginal private/social benefit
- The free-market output where MPC = MPB
- The socially efficient output where MSC = MSB
The deadweight loss is the welfare lost between the two output levels. It is usually a triangle.
If the marking scheme mentions a diagram, draw it. If it does not, do not force one in.
A chain that earns analysis marks
Question: Explain why negative externalities cause market failure.
Negative externalities of production mean that the social cost of producing a good is higher than the private cost to the firm. Because the firm does not pay for the external cost, it produces at a lower private cost, so it supplies more than the socially efficient quantity. At this higher output, the marginal social cost exceeds the marginal social benefit, so each extra unit creates a welfare loss. The result is a deadweight loss, which means resources are overallocated to this good.
Four connected steps. This is what analysis looks like.
Common lost marks
- Defining market failure without applying it. Define it, then use it in the context of the question.
- Listing causes without explaining one. A 20-mark essay needs depth, not a list of six causes.
- Drawing a diagram without explaining it. A diagram alone is not analysis. State the shift and the outcome in words.
- Ignoring the question's good. Use the specific market in the question, not a generic example.
- Confusing market failure with government failure. They are different. Government failure is when intervention makes things worse.
Evaluation angles
When asked to evaluate, use these:
- Size of the externality — is the deadweight loss large or small?
- Measurement — can the government value the external cost accurately?
- Elasticity — how much does behaviour change?
- Government failure — could intervention create a worse outcome?
- Time — does the policy work before the damage is done?
Quick check
Can you answer these without notes?
- Define market failure in one sentence.
- Name three causes.
- Explain one chain from cause to deadweight loss.
- Give one reason a government policy might fail.
If you can, you are ready to write a 20-mark answer on this topic.