Market Failure

Market failure occurs when the competitive market equilibrium is not Pareto efficient — some mutually beneficial trades fail to occur, or resources are misallocated. In the context of Asymmetric Information, the mechanism is clear: when buyers cannot distinguish high-quality from low-quality sellers, they offer only an average-quality price; high-quality sellers find that price below their reservation value and exit; average quality in the pool falls; price falls further; and the cycle continues until the market collapses to a lemons-only equilibrium or disappears entirely. Every car in the Akerlof example has a positive gain from trade, but only lemons survive — an unambiguous market failure.

Asymmetric information is one of several sources of market failure covered in this course (others include externalities and public goods). See Topic 1 — Asymmetric Information for the adverse selection death spiral mechanism.

When to use

Identify market failure whenever private information creates a wedge that prevents efficient trades from occurring. In exam questions, the key signal is a situation where all types have a positive surplus from trade but the equilibrium excludes the highest-quality types — that is the fingerprint of adverse-selection-driven market failure. Adverse Selection and Moral Hazard are the two main asymmetric-information channels through which markets fail in this topic.