Demerit Goods
Definition
Demerit good: a good that is over-consumed because consumers have imperfect information about its true harm, and which a negative value judgement holds society should consume less of, for example cigarettes or alcohol.
- The label also carries a negative value judgement that less of the good ought to be consumed.
- Tobacco, alcohol and gambling are common examples, because the pleasure is immediate but the harm arrives slowly and is easy to discount.
Key Idea
- The demerit-good case rests on imperfect information, reinforced by a value judgement.
- A demerit good is rival and excludable, unlike a public good.
- Consumption often also creates negative externalities, so social cost exceeds private cost.
The Over-Consumption Chain
- At the point of choice, consumers act on the private benefit they perceive.
- Imperfect information means the long-term harm to themselves is underweighted.
- Perceived benefit therefore lies above the actual benefit.
- Acting on the inflated perceived benefit, consumers demand more than the amount that reflects the true benefit.
- So the market delivers more than the socially optimal quantity.
Example
- Consider cigarettes sold on the private market.
- Many smokers underestimate the long-term damage to their own health.
- Because the perceived benefit is high, more cigarettes are bought than is socially desirable.
- Second-hand smoke also imposes an external cost on others nearby.
- Both effects push consumption above the social optimum, so the good is over-consumed.
Perceived versus Actual Benefit
- A diagram can show how poor information moves consumption away from the optimum.
- It contrasts the perceived private benefit with the actual private benefit.
- When the benefit is overrated, the perceived benefit curve lies above the true benefit curve.
- The market then over-consumes, and the welfare loss is the area between the market outcome and the social optimum.
Policy Choices
- A ban looks decisive but can push activity into an illegal black market.
- An indirect tax, such as £6 of duty per packet, raises price and cuts consumption while preserving some choice.
- Information campaigns correct the imperfect information at its source, closing the gap between perceived and actual benefit.
- On balance, many economists favour taxes and better information over outright bans, though the best mix depends on how addictive the good is.
Exam technique
- Explain over-consumption through both overvaluation and imperfect information.
- Draw and label the perceived and actual benefit curves and shade the welfare loss.
- A correctly labelled diagram earns the analysis marks.
Common Mistake
- Do not assume a demerit good should simply be banned.
- Bans ignore black-market effects and wider welfare trade-offs.
- Do not treat demerit goods and public goods as the same thing.
- Demerit goods are rival and excludable and are defined by imperfect information.
Self review
- Define a demerit good.
- Explain why imperfect information leads to over-consumption.
- Give one example and its external cost.
- Explain how perceived benefit differs from actual benefit on a diagram.
- Explain why an outright ban is not always the best policy.
