Exchange Economies and Externalities

Exchange can benefit its participants while leaving consequential effects on others outside the decision’s costs and benefits.

An exchange reallocates resources between parties. An externality occurs when an action affects someone else’s welfare or production possibilities in a way the decision maker does not fully take into account through the transaction. A buyer and seller can both benefit while neighbors bear an unpriced cost, or while others receive an uncompensated benefit.

In a standard competitive model, unpriced marginal harm can produce too much of an activity relative to the efficient level, while an unpriced benefit can produce too little. These conclusions depend on the surrounding assumptions and other distortions. Negotiation, rules, incentives, design changes, and public action are possible responses, each with information and implementation costs. Externalities are one source of market failure; they are not the only one.

When to use it

Useful when an apparently beneficial transaction or local decision imposes unaccounted costs or benefits elsewhere.

How it can help

Make affected third parties visible and compare ways to account for the spillover.