Asymmetric information

Most deals are struck between parties who know different things, and the gap between what each knows shapes the outcome more than the price does.

Asymmetric information exists when one party to a transaction has more or better information than the other. This imbalance, far from being a minor friction, distorts markets in systematic ways, and recognising it transformed economics, revealing why many markets fail or behave strangely.

The informed and the uninformed

In the idealised market, everyone has full information. In reality, sellers usually know more about their products than buyers, borrowers more about their own riskiness than lenders, employees more about their effort than employers, the insured more about their own habits than insurers. This gap in knowledge means the less-informed party cannot fully judge what they are getting, and the better-informed party can exploit, or be suspected of exploiting, that advantage.

Two characteristic problems

Asymmetric information produces two classic problems, depending on when the hidden information matters. Adverse selection arises before a transaction, when the uninformed party cannot tell good from bad and so attracts the worst, as in insurance, where the unhealthy are keenest to buy. Moral hazard arises after a transaction, when one party's hidden actions change once they are protected, as when the insured take more risk. Both stem from one side knowing what the other cannot observe.

How markets cope

Because asymmetric information can cause markets to function poorly or even collapse, much economic activity is devoted to coping with it. Signalling lets the informed party prove what it knows through costly action; screening lets the uninformed party design choices that make the informed reveal themselves; warranties, reputations, certifications, and intermediaries all exist partly to bridge information gaps. A great deal of institutional design is, at bottom, machinery for managing the fact that people know different things.

Asymmetric information is one of the most important ideas in modern economics, the recognition that the distribution of knowledge, not just its content, shapes markets. It explains why so many real markets depart from the textbook ideal, why trust and reputation matter so much, and why much of commerce is built around the simple, pervasive fact that the two sides of a deal rarely know the same things.