Merit and demerit goods

1. A free market misjudges how much of certain goods people should consume, because consumers act on imperfect information about the true costs and benefits.

Why markets get it wrong

1. Consumers act on imperfect information about the long-term costs and benefits of what they consume.
2. With a demerit good they underestimate the private and external costs, so they demand more than is socially desirable.
3. With a merit good they underestimate the private and external benefits, so they demand less than is socially desirable.
4. These goods also generate externalities, so the gap between private and social valuations widens and the market outcome misallocates resources.

Correcting over-consumption

1. The government discourages a demerit good by raising its price or restricting its use.
2. An indirect tax raises the price, so quantity demanded contracts along the demand curve towards the optimum.
3. Regulation and bans limit availability directly, while information campaigns correct the imperfect information at its source.

Correcting under-consumption

1. The government encourages a merit good by lowering its price or raising its provision.
2. A subsidy cuts the price, so quantity demanded extends along the demand curve towards the optimum.
3. Direct state provision free at the point of use, plus information campaigns, reveals benefits consumers had underestimated.

Getting the dose right

1. Intervention works only if it moves consumption towards the socially optimal level.
2. Too small a tax or subsidy leaves the failure uncorrected.
3. Too large a tax or subsidy over-corrects and creates a new misallocation, so the size of the intervention matters and depends on how accurately the optimum is estimated.

How effective is this intervention?

1. Used well, these tools do shift consumption the right way, because a tax on a demerit good raises its price and contracts quantity demanded, a subsidy on a merit good lowers its price and extends quantity demanded, and both also raise revenue or reveal benefits, so the failure is at least partly corrected.
2. How much consumption actually changes depends on price elasticity of demand, and many demerit goods such as tobacco and alcohol are addictive and price-inelastic, so even a large tax cuts consumption only a little in the short run, mainly raises revenue, and falls hardest on low-income consumers, though the response is larger over a longer time horizon.
3. Heavy taxes and outright bans can also push trade into black markets that escape control, information campaigns work slowly and only if people act on them, and the optimum itself is uncertain, so intervention can under- or over-correct and carries administrative and enforcement costs.
4. On balance, intervention is justified where the gap between private and social valuations is large and the good is clearly a merit or demerit good, but its real impact depends on the elasticity of demand, the time horizon, how well the tax or subsidy is calibrated to the optimum, and enforcement, so a package that combines price measures with information and regulation usually works better than any single tool.