Market failure and the marginal toolkit

Market failure occurs when the free market, left alone, misallocates resources — producing too much of some goods and too little of others, so welfare is not maximised. It is a failure of allocative efficiency. (Partial market failure = the good is provided, but in the wrong quantity. Complete market failure = a missing market; no one supplies it at all.)

An externality is a cost or benefit imposed on a third party — someone not involved in the transaction — that is not reflected in the market price. Everything runs on four terms:

• MPC — marginal private cost: what it costs the producer to make one more unit.
• MEC — marginal external cost: what that unit costs third parties.
• MSC = MPC + MEC — marginal social cost: the full cost to society.
• Likewise MSB = MPB + MEB on the benefit side.

Because private agents only ever weigh up their own costs and benefits, the market equilibrium sits at MPC = MPB. Wherever there is an externality, that is not the socially optimal point, and the difference between them is the welfare loss (deadweight loss) triangle.

Negative production externality

The four externality diagrams

OCR asks for externalities in production and in consumption, each of which can be negative or positive. Get the four straight:

• Negative production externality (factory pollution). MSC > MPC, so the MSC curve lies above MPC. Free market overproduces; welfare loss triangle sits between the two quantities and between the MSC and MSB curves.
• Positive production externality (a firm's R&D that rivals learn from; training workers who later move on). MSC < MPC. The market underproduces.
• Negative consumption externality (smoking, alcohol, driving in a city). MPB > MSB, so the true social benefit curve lies below private benefit. The market overconsumes.
• Positive consumption externality (vaccination, education). MSB > MPB. The market underconsumes.

Rule of thumb: if the externality is negative, the market does too much. If it is positive, the market does too little. The welfare loss triangle always has its point at the social optimum and opens out towards the free-market quantity.

Your turn — welfare loss

Your turn — marginal social cost

Positive consumption externality

Public goods and the free-rider problem

A public good has two defining characteristics (OCR adds two more):

• Non-excludable — once provided, you cannot stop anyone consuming it (you cannot switch off the streetlight for one household).
• Non-rival / non-diminishable — one person's consumption does not reduce the amount available to anyone else.
• Non-rejectable — you cannot refuse it (national defence protects you whether you like it or not).
• Zero marginal cost — supplying one extra consumer costs nothing.

Because the good is non-excludable, every consumer has the incentive to free-ride: enjoy it without paying, since they cannot be excluded if they refuse. If everyone reasons this way, revenue is zero, no private firm can profitably supply it, and the market provides nothing at all — a missing market and a case of complete market failure. The state therefore provides public goods and funds them through taxation (which is compulsory precisely to defeat free-riding).

A private good is excludable and rival (a sandwich). A quasi-public good has the characteristics only partly: a road is non-excludable and non-rival when empty, but becomes rival when congested and excludable once you install toll gates or number-plate cameras — technology changes the classification.

Your turn — net social benefit of a public good

Is it a public good?

Information failure, merit and demerit goods

The competitive model assumes perfect information. In reality information is imperfect, and often asymmetric — one party knows more than the other.

• Asymmetric information → adverse selection: a used-car seller knows the car is a lemon; the buyer does not, so offers only an average price; good cars are withdrawn; quality collapses (Akerlof's "market for lemons"). Similarly, the people most likely to claim buy the most insurance.
• Moral hazard — once insured, a party takes more risk because they no longer bear the full cost. Fully insured banks lend recklessly; a fully insured cyclist locks the bike less carefully.

Merit good — a good whose private benefits are underestimated by the consumer and which generates positive externalities: education, healthcare, pensions, exercise. It is underconsumed in a free market, so the state subsidises or provides it, often free at the point of use, and sometimes compels it (school to 18).

Demerit good — a good whose private costs are underestimated by the consumer and which generates negative externalities: tobacco, alcohol, gambling, sugary drinks. It is overconsumed, so the state taxes, regulates, restricts advertising, or bans it.

Note the value judgement. Calling something a merit or demerit good is a normative claim — someone is deciding that consumers are mis-valuing their own welfare. That is a paternalist argument, and it is precisely why libertarians resist sugar taxes. Behavioural economics strengthens the case (present bias means people really do under-weight future harm), but it does not remove the value judgement.

Why is a merit good underconsumed?

Moral hazard or adverse selection?

The social optimum

The other sources of market failure

Externalities, public goods and information failure are the headline cases, but the specification expects you to see market failure as a family of problems:

• Monopoly power — a firm with market power restricts output and raises price above marginal cost, so P > MC and allocative efficiency is lost. (Component 1, market structures.)
• Factor immobility — labour that is occupationally immobile (a redundant miner cannot code) or geographically immobile (housing costs, family ties) means resources do not flow to where they are most valued. Structural unemployment persists even with vacancies unfilled.
• Inequality — the market rations by ability to pay. That may be efficient, but a distribution in which some cannot afford basic goods is a failure of equity, and OCR expects you to distinguish the two.
• Missing markets — no one can profitably supply the good at all (pure public goods; insurance against being born with a disability).
• Common access resources — non-excludable but rival: ocean fish stocks, the atmosphere. Each user takes as much as they can because anything they leave, someone else takes. The result is the tragedy of the commons, and it is the deep structure of the climate problem.

From diagnosis to prescription

Every intervention you meet in the next lesson is an attempt to close a gap you have now identified:

• Negative externality → make the polluter pay: an indirect tax equal to the MEC at the social optimum, a tradable permit scheme, or regulation. The aim is to internalise the externality — to force MPC up onto MSC.
• Positive externality / merit good → subsidy, state provision, or information provision to raise MPB towards MSB.
• Public good → state provision funded by taxation, because free-riding makes the private market impossible.
• Information failure → compulsory disclosure (nutrition labels, MOT certificates, financial advice rules) or nudges.

But hold the applause. Every one of these interventions requires the government to know the size of the externality — to put a number on the marginal external cost of a tonne of carbon or a pint of beer. It rarely does. Valuation errors, unintended consequences and political capture are why government failure is the other half of this story.

Negative, positive, or a public good?

Tap a card, then tap the type of market failure it illustrates.

Match the marginal concept to its definition

Tap an item on the left, then its partner on the right.

The big ideas to know

You've now covered market failure and externalities from the OCR A-level Economics (H460) specification. Press Finish to see your score.