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Glossary · Game Theory

Costly Signaling

also: signaling theory · signalling · signaling · Spence signaling · advertising as a signal · money burning

Definition

Costly signaling is the transmission of private information through an action that is cheaper for a high-quality sender than for a low-quality one, so that imitation does not pay. Spence (1973) formalized it for education; Nelson (1974) and Milgrom and Roberts (1986) applied it to advertising, where visible spend tells buyers a firm expects the repeat purchases only a good product earns.

A signal separates types only when the single-crossing condition holds: the marginal cost of sending it must be lower for the type the receiver wants to identify. Education works as a signal in Spence's model because it is less painful for the able. Advertising works as a signal in Nelson's and in Milgrom and Roberts's models not because of what it says but because of what it costs, since only a firm expecting repeat business can recoup a lavish launch. The same logic covers warranties, money-back guarantees, prestige office addresses, sponsorship, and conspicuous engineering investment. The failure modes are equally instructive: when the cost is equal for all types the signal pools and conveys nothing, and when receivers cannot observe the cost the spend is wasted.

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