Why can a free market produce too much of some goods and too little of others?
Explain market failure and externalities, distinguishing external costs from external benefits
A clear O-Level answer on market failure and externalities. Why free markets can over-produce goods with external costs and under-produce goods with external benefits, with clear examples and the case for intervention.
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What this dot point is asking
The syllabus wants you to explain what market failure is, define externalities, and distinguish external costs from external benefits. The big idea is that free markets work well in many cases, but sometimes they fail to produce the amount of a good that is best for society, because the people deciding ignore the effects of their actions on others.
The answer
What market failure means
A market can be efficient for the buyer and seller yet still fail society, because their decisions ignore effects on third parties.
What an externality is
When a buyer and seller make a deal, they consider only their own private costs and benefits. Any effect on others, the externality, is ignored, which is what causes the market to fail.
External costs lead to over-production
An external cost is a harm imposed on third parties. For example, a factory that pollutes a river imposes a cost on the people downstream, who are not buying its product. Because the firm ignores this cost and counts only its own private costs, it produces more than the amount that is best for society. So goods with external costs tend to be over-produced.
External benefits lead to under-production
An external benefit is a gain enjoyed by third parties. For example, a person who gets vaccinated also protects others from catching the disease. Because the buyer ignores this benefit to others and counts only their own private benefit, less is produced and consumed than is best for society. So goods with external benefits tend to be under-produced.
Why this justifies intervention
Because the market over-produces goods with external costs and under-produces goods with external benefits, there is a case for the government to step in: to discourage the first (for example, by taxing pollution) and to encourage the second (for example, by subsidising vaccination). The aim is to move output toward the amount that is best for society.
Examples in context
Example 1. Traffic congestion in Singapore. A driver who joins a busy road imposes an external cost on every other road user, by adding to congestion and slowing them down. Because each driver ignores this cost to others, there is too much driving. Singapore tackles this with road pricing (ERP), which makes drivers pay for the congestion they cause.
Example 2. Education's external benefits. When a person becomes better educated, they gain higher earnings, but society also benefits from a more skilled, productive and law-abiding population. Because individuals ignore this external benefit, education would be under-consumed if left to the market, which is why governments subsidise and provide it.
Try this
Cue. Define an externality. A cost or benefit of an economic activity that falls on a third party who is not part of the decision to produce or consume.
Cue. Explain why a good with external costs is over-produced by the market. The producer counts only its own private costs and ignores the cost imposed on third parties, so the true cost to society is higher than the cost faced, and more is produced than is best for society.
Cue. Give one example of an external benefit and state its effect on output. Vaccination protects others from disease (an external benefit); because individuals ignore this benefit to others, the market under-produces it.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original6 marksExplain, using the idea of external costs, why a free market produces too much of a good such as electricity generated by burning coal.Show worked answer →
A 6 mark question rewards the definition of an external cost and the over-production reasoning.
- External cost
- An external cost is a cost of an activity that falls on third parties who are not part of the decision. Burning coal to make electricity creates pollution that harms the health of nearby residents, who are not buying the electricity.
- Why over-production results
- The firm only counts its own private costs (fuel, labour, plant) when deciding how much to produce, and ignores the pollution cost borne by society. Because the true cost to society is higher than the private cost, the market produces more than the amount that is best for society.
- Conclusion
- The free market over-produces the good, because the external cost is not paid by the producer or the consumer. This is a market failure that may justify government action, such as a tax.
Markers reward the definition of an external cost, the point that firms ignore costs they do not pay, and the conclusion that the good is over-produced relative to the socially best amount.
Original5 marksDistinguish between an external cost and an external benefit, giving an example of each.Show worked answer →
A 5 mark question rewards both definitions, each with a clear example.
- External cost
- An external cost is a cost of an activity that falls on third parties not involved in the decision. An example is the pollution from a factory that harms nearby residents.
- External benefit
- An external benefit is a benefit of an activity that is enjoyed by third parties not involved in the decision. An example is a person being vaccinated, which also protects others from catching the disease.
- Key contrast
- An external cost harms third parties and tends to lead to over-production; an external benefit helps third parties and tends to lead to under-production, because the decision-maker ignores effects on others.
Markers reward both definitions with the third-party idea, a correct example of each, and ideally the link to over- and under-production.
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