How Imperfect Information Causes Market Failure

Question

Explain how imperfect information can result in market failure of different products. [10]

Answer

Information failure arises when economic agents lack perfect information and so cannot make optimal decisions, producing an inefficient allocation of resources and hence market failure. It takes two forms: consumer ignorance (a species of imperfect information) and asymmetric information. This essay explains each in turn through a distinct product. (Information failure is examined in prose under 9570; there is no associated diagram.)

Consumer ignorance. When consumers hold incorrect or insufficient information about a good, they mis-estimate the marginal private benefit ($MPB$) they derive from it. Take cancer screening: consumers’ perceived $MPB$ falls below their actual $MPB$ because, through ignorance, they do not appreciate that cancer is among the leading causes of death and that early screening materially improves outcomes — so $MPB_{\text{actual}}$ lies above $MPB_{\text{perceived}}$.

The marginal private cost ($MPC$) of screening — kits, medical staff, facilities — is the market supply curve, while $MPB$ is the demand curve. Deciding on perceived benefit, consumers transact at $Q_m$ where $MPB_{\text{perceived}} = MPC$. Had they known the true benefit, they would have consumed the larger $Q_{m'}$ where $MPB_{\text{actual}} = MPC$. The ignorance therefore causes an under-consumption of $Q_{m'} - Q_m$. Over that range, the additional private benefit forgone exceeds the additional private cost forgone, so a deadweight welfare loss arises — resources are under-allocated to cancer screening, and the market fails.

Asymmetric information. Asymmetric information arises when the two parties to a transaction do not share the same knowledge, distorting incentives and producing inefficient outcomes. Its two forms differ in when the opportunism occurs.

• Adverse selection — opportunism before the transaction. In the used-car market, dealers (the more-informed party) know each car’s true condition but will not reveal it, harming buyers (the less-informed party). Anticipating that they may receive a low-quality car, buyers price in the risk and will pay only a lower price. At that lower price, owners of genuinely high-quality used cars withdraw, leaving disproportionately many “lemons”. The market for high-quality used cars unravels and ceases to exist — a market failure.

• Moral hazard — opportunism after the transaction. In the health-insurance market, an insured consumer (now the more-informed party) knows their own behaviour better than the insurer who sold the cover. Once insured, the consumer is less incentivised to stay healthy, and the insurer bears the cost of that negligence. Because insurers cannot prevent post-contract changes in behaviour, fewer firms supply insurance, and the quantity transacted falls below the social optimum — again, market failure.

Conclusion. Imperfect information causes market failure through three channels — consumer ignorance, adverse selection, and moral hazard — each leading agents to a quantity that departs from the socially optimal one, and so to a misallocation of resources.