What market failure is and its sources

Meaning

Market failure occurs when the free market leads to a misallocation of resources: too much or too little of a good is produced and consumed compared with the socially optimal level, so society's welfare is not maximised.

The socially optimal output is where marginal social benefit = marginal social cost (MSB = MSC). A free market produces where private benefit equals private cost, ignoring effects on others.

Types:

• Complete market failure: no market exists at all (a 'missing market'), as with public goods.
• Partial market failure: the market exists but produces the wrong quantity or price, as with externalities.

Sources named in the specification

• Externalities: costs or benefits to third parties that the market ignores (pollution, education).
• Under-provision of public goods: the free-rider problem means firms cannot make people pay (street lighting, defence).
• Information gaps: buyers or sellers lack full information (second-hand cars, healthcare, pensions).
• Moral hazard: people take more risks because someone else bears the cost (insurance, banks).
• Speculation and market bubbles: prices rise far beyond underlying value, then crash (housing, shares).

Exam technique

When asked to 'explain why X is a market failure', name the source, explain the mechanism (who is affected and why the market ignores it) and state the result: over-production or under-production relative to the social optimum. Then, if there are evaluation marks, discuss how significant the failure is and whether intervention would improve it.

Worked example

Explain why the free market might under-produce vaccinations.

1. Source: a positive externality of consumption.
2. A vaccinated person also protects others, a benefit to third parties that the buyer does not take into account.
3. So private benefit is less than social benefit and individuals buy fewer vaccinations than the social optimum.
4. Resources are misallocated: too few vaccinations.

Answer: Positive externalities mean demand reflects only private benefit, so output is lower than the socially optimal level.

Check yourself

1. Market failure occurs when
   • a firm makes a loss
   • prices rise
   • the government intervenes in a market
   • the free market allocates resources inefficiently compared with the social optimum
   Show answer

   the free market allocates resources inefficiently compared with the social optimum. The key idea is misallocation of resources.

2. A public good such as national defence is an example of
   • partial market failure
   • complete market failure (a missing market)
   • a free good
   • an inferior good
   Show answer

   complete market failure (a missing market). Without intervention, the market may not provide it at all.

3. Which is NOT a source of market failure listed in the specification?
   • Externalities
   • Imperfect information
   • Speculation and market bubbles
   • Rising consumer incomes
   Show answer

   Rising consumer incomes. Rising incomes shift demand but do not in themselves cause misallocation.

4. The socially optimal level of output is where
   • marginal social benefit equals marginal social cost
   • marginal private benefit equals marginal private cost
   • total revenue is maximised
   • price equals zero
   Show answer

   marginal social benefit equals marginal social cost. Society's welfare is maximised when MSB = MSC.

5. A factory's pollution causes the market to over-produce its product. This is
   • complete market failure
   • a public good
   • partial market failure
   • allocative efficiency
   Show answer

   partial market failure. The market exists but produces too much.

6. Explain what is meant by market failure.
   Show answer

   Market failure is when the free market misallocates resources, producing too much or too little of a good compared with the socially optimal level, so society's welfare is not maximised.. Misallocation plus comparison with the social optimum.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Economics specification (2018)

Last updated 8 November 2026. Spotted a mistake? Tell us.