Signalling (or signaling; see spelling differences) is a theory of decision-making and communication under imperfect or incomplete information. It describes situations in which a signaler uses observable actions, attributes, or communications (signals) to convey credible information about otherwise unobservable qualities to a receiver. Signals are most credible when they are differentially costly (i.e., harder or more expensive for low-quality signalers to produce or imitate than for high-quality signalers). Signaling theory is about decision-making and communication under incomplete information. It describes situations in which signalers send observable actions, attributes, or communications that carry credible information about unobservable qualities that matter for a receiver’s choice. Signals are most informative when they are differentially costly, meaning they are highly costly for low-quality signalers and less costly for high-quality signalers. In many applications, the signaling system is analysed in terms of the signaler, the signal, the receiver, and the costs embedded in producing, maintaining, or imitating the signal. Costs may include direct production costs, penalties for false or misleading signaling, and “reaction costs” that arise when unintended audiences respond negatively to a signal intended for someone else. Signals can also be sent unintentionally, so observable behaviour may still inform receiver decision-making even when it was not designed as deliberate communication. Signalling was briefly introduced and discussed in the seminal Theory of Games and Economic Behavior, which is considered to be the text that created the research field of game theory. Signaling theory was more fully developed by Michael Spence, specifically in the context of observed knowledge gaps between organisations and prospective employees. However, its intuitive nature led it to be adapted to many other domains, such as Human Resource Management, business, and financial markets. Later reviews emphasise additional actors and complexities in signaling systems (including broader stakeholder audiences) and propose directions for future theory development. In Spence's job-market signaling model, (potential) employees send a signal about their ability level to the employer by acquiring education credentials. The informational value of the credential comes from the fact that the employer believes the credential is positively correlated with having the greater ability and difficult for low-ability employees to obtain. Thus the credential enables the employer to reliably distinguish low-ability workers from high-ability workers. The concept of signaling is also applicable in competitive altruistic interaction, where the capacity of the receiving party is limited.
Introductory questions Signalling started with the idea of asymmetric information (a deviation from perfect information), which relates to the fact that, in some economic transactions, inequalities exist in the normal market for the exchange of goods and services. In his seminal 1973 article, Michael Spence proposed that two parties could get around the problem of asymmetric information by having one party send a signal that would reveal some piece of relevant information to the other party. The receiver interprets the signal, updates beliefs about the signaler’s unobservable quality, and adjusts a selection decision accordingly (e.g., hiring, partnering, investing, contracting, or pricing). Analyses typically specify which unobservable construct the signal is meant to proxy (such as ability, commitment, or future cash flows) and why the signal should align with that construct in the context at hand. Because multiple unobserved factors can jointly create information asymmetry, signaling accounts often clarify how a particular signal reduces that asymmetry rather than treating the information gap as a single, undifferentiated variable. There are, of course, many problems that these parties would immediately run into.
Effort: How much time, energy, or money should the sender (agent) spend on sending the signal? Reliability: How can the receiver (the principal, who is usually the buyer in the transaction) trust the signal to be an honest declaration of information? Stability: Assuming there is a signalling equilibrium under which the sender signals honestly and the receiver trusts that information, under what circumstances will that equilibrium break down?
Job-market signalling In the job market, potential employees seek to sell their services to employers for some wage, or price. Generally, employers are willing to pay higher wages to employ better workers. While the individual may know their own level of ability, the hiring firm is not (usually) able to observe such an intangible trait—thus there is an asymmetry of information between the two parties. Education credentials can be used as a signal to the firm, indicating a certain level of ability that the individual may possess; thereby narrowing the informational gap. This is beneficial when the signal helps the receiver infer a relevant unobservable quality. Some observable attributes (e.g., background information the applicant cannot easily change) are better treated as indices or as inputs to screening rather than as strategic signals; in such cases, the receiver may be using observed information to screen options rather than the sender intentionally signaling Furthermore, signaling can sometimes be detrimental in the educational scenario, when heuristics of education get overvalued such as an academic degree, that is, despite having equivalent amounts of instruction, parties that own a degree get better outcomes—the sheepskin effect. In many labor-market settings, the intensity of education, certification, or disclosure can vary by degree, so signaling costs and receiver reactions may be continuous rather than a simple divide between “signalers” and “non-signalers”.
Spence 1973: "Job Market Signaling" paper
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