Edexcel A-Level Economics A (9EC0) · Theme 1
Specification points
- Types of market failure: externalities, public goods and information gaps.
- Positive and negative externalities in production and consumption.
- Merit and demerit goods; the free-rider problem.
- Symmetric and asymmetric information.
What is market failure?
Market failure occurs when the free market fails to allocate resources efficiently, so social welfare is not maximised. The main causes are externalities, public goods and information gaps.
Externalities
An externality is a cost or benefit to a third party. The key is the gap between private and social costs/benefits:
- Social cost = private cost + external cost; social benefit = private benefit + external benefit.
- Negative externalities (pollution) → the market over-produces/over-consumes; welfare loss occurs where MSC ≠ MSB.
- Positive externalities (education, vaccination) → the market under-provides.
Negative externalities → overproduction; positive externalities and merit goods → underconsumption.
Key definitions
| Term | Definition |
|---|---|
| Externality | A cost or benefit affecting a third party outside the transaction. |
| Public good | A good that is non-rival and non-excludable, causing the free-rider problem. |
| Merit good | A good under-consumed because its private/external benefits are undervalued. |
| Asymmetric information | When one party in a transaction has more information than the other. |
Public goods
Public goods are non-rival and non-excludable, so people can free ride and firms cannot charge — the market fails to provide them (defence, street lighting). This justifies government provision funded by taxation.
Merit, demerit goods and information gaps
- Merit goods are under-consumed and demerit goods over-consumed because consumers misjudge the true costs and benefits.
- Asymmetric information (e.g. a seller knowing more than a buyer) leads to a misallocation, such as the "market for lemons" in used cars.
Worked example
A factory emits pollution: marginal social cost exceeds marginal private cost, so output exceeds the social optimum, creating a welfare loss. The market ignores the external cost, over-allocating resources to the polluting good — a clear negative production externality requiring intervention (Theme 1.4).
Common exam mistakes
- Confusing merit goods (under-consumed) with public goods (non-excludable).
- Mislabelling the welfare-loss area on MSC/MSB diagrams.
- Treating any information problem as asymmetric — it must be *unequal* between parties.
Exam technique
Draw the correct externality diagram, mark the market and social optima, and shade the welfare loss. Distinguish clearly between the three causes of market failure.
Quick revision
- Causes: externalities, public goods, information gaps.
- Social cost/benefit = private + external.
- Public goods: non-rival, non-excludable → free-rider problem.