What is market failure?

In 1.2 the price mechanism looked flawless: prices ration, signal and incentivise, and total welfare (consumer + producer surplus) is maximised at equilibrium. That result only holds if all costs and benefits are captured in the price.

They often are not. Edexcel names three causes:

• Externalities — costs or benefits that spill over onto third parties and are not in the price.
• Under-provision of public goods — goods the market will not supply at all.
• Information gaps — buyers or sellers do not know the true costs and benefits.

Complete vs partial failure. Partial market failure: the market provides the good, but in the wrong quantity (too much petrol, too little education). Complete market failure: a missing market — the market provides none of it (national defence).

Private, external and social

• Private cost — the cost borne by the producer or consumer of the good (the firm's wages, raw materials, energy).
• External cost — the cost imposed on third parties who are not part of the transaction (asthma from the factory's emissions).
• Private benefit — the benefit to the buyer/seller. External benefit — the spillover benefit to third parties.

At A-level we work at the margin: MPC, MEC, MSC; MPB, MEB, MSB. An externality is simply the gap between the private and social curve. If MEC = 0 and MEB = 0, there is no externality and the market gets it exactly right.

Whose value judgement? Putting a money figure on a life shortened by air pollution, or on a river's ecosystem, requires a normative valuation (1.1.2). This is the single best evaluation point in the whole topic: externalities are real, but their magnitude is estimated, contested and often wrong.

Your turn — marginal social cost

Negative externality of production

The firm ignores the pollution it imposes, so it only counts MPC. It produces where MPB = MPC at Q₁. Society wants MSB = MSC at Q*. Because MSC lies above MPC, the market over-produces: Q₁ > Q*.

Why a triangle? Between Q* and Q₁ every unit produced costs society (MSC) more than it benefits society (MSB). Summing that gap over the excess units gives the welfare loss. Its area = ½ × base × height, where base = Q₁ − Q*, and height = the vertical gap between MSC and MSB at Q₁ (equal to the external cost per unit).

Your turn — welfare loss

Positive externality of consumption

Now the benefit spills over. A vaccinated person gains protection (MPB), but also reduces everyone else's risk of infection (MEB) — herd immunity. Consumers only count their private benefit, so they consume at MPB = MSC (Q₁). Society wants MSB = MSC (Q*). Because MSB lies above MPB, the market under-consumes: Q₁ < Q*.

Impact on economic agents (1.3.2e). Third parties bear uncompensated costs or gain uncompensated benefits. Producers of the polluting good enjoy artificially low costs and so over-produce. Consumers of the merit good under-consume because they cannot capture the spillover. Government sees a case to intervene — with a tax, a subsidy, regulation or provision (all of Theme 1.4).

Your turn — potential welfare gain

Match the example to the type of externality

Ask two questions: is the spillover a cost or a benefit, and does it come from the act of producing or the act of consuming?

Reading the diagram

Public goods and the free rider problem

A pure public good has two properties:

• Non-rival — one person consuming it does not reduce the amount available to anyone else. Your enjoyment of national defence does not use any of it up. Marginal cost of supplying one more consumer = zero.
• Non-excludable — once provided, it is impossible (or prohibitively costly) to stop anyone consuming it, including those who did not pay.

A private good is the opposite: rival and excludable (a sandwich). A quasi-public good has one property but not the other — a toll road is excludable but (until congested) non-rival; a public beach is effectively non-excludable but rival once crowded.

Because the good is non-excludable, every rational consumer has an incentive to understate their willingness to pay and consume for free. If everyone free-rides, no revenue is raised, so no profit-seeking firm will supply it. This is complete market failure — a missing market. The good is not under-provided; it is not provided at all. Hence state provision, funded through taxation (1.4.1b).

Evaluation: technology changes the boundary. Broadcast TV was once close to a public good; encryption made it excludable and a private market appeared. Whether something is a public good is therefore not fixed — it depends on the technology of exclusion.

Sort the goods

Test each good against both criteria: is it rival? Is it excludable?

The free rider problem

Symmetric and asymmetric information

The rational-choice model of 1.2.1 assumes agents have perfect information about costs and benefits. In reality:

• Symmetric information — buyer and seller know the same things. The market can clear efficiently.
• Asymmetric information — one side knows more. The used-car seller knows the car is a lemon; you do not. The person buying health insurance knows they are ill; the insurer does not.

How this misallocates resources:

• Over-consumption of goods whose private costs are understated: consumers systematically underestimate the long-run harm of smoking, gambling and junk food (a demerit good). They would buy less if fully informed.
• Under-consumption of goods whose private benefits are understated: people underestimate the lifetime return to education, training and pension saving (a merit good).
• Adverse selection — if buyers cannot tell good cars from lemons, they will only pay an average price; owners of good cars withdraw, quality falls further, and the market can unravel completely (Akerlof, 1970).

Merit and demerit goods are a combination: education is a merit good because of both a positive externality (a more productive workforce) and an information gap (individuals undervalue it). That is why Edexcel wants you to name both failures — the policy fix differs: an externality calls for a subsidy, an information gap calls for provision of information.

Information failure

How to evaluate market failure

• Magnitude. Every market has some spillover. The policy question is whether the externality is big enough to justify intervention. A tiny welfare loss triangle may cost more to correct than it is worth.
• Measurement. MEC and MEB are estimates, produced by valuation techniques that rest on value judgements. Get the number wrong and you set the tax at the wrong level — and create government failure (1.4.2).
• The Coase counter-argument. If property rights are clear and bargaining is cheap, the parties can negotiate a solution privately without the state. In practice, with millions of affected third parties (climate change), transaction costs make this impossible.
• Short run vs long run. Demand for petrol is inelastic in the short run, so a pollution tax barely cuts output at first — but over years consumers switch to EVs. Judging the policy on year-one data is a trap.

The killer line: "market failure is a necessary condition for intervention, but not a sufficient one — the state must be able to correct it at a lower welfare cost than the failure itself."

Judging the case for intervention

The big ideas to know

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