Information Economics: Adverse Selection, Moral Hazard, and Signaling

Information Economics: Adverse Selection, Moral Hazard, and Signaling

Overview

Information economics studies how asymmetric information between parties causes market failures and shapes institutional responses. Akerlof's "market for lemons" shows adverse selection can collapse entire markets; Spence's signaling model shows informed parties can credibly convey quality through costly actions; Rothschild-Stiglitz screening shows uninformed parties can design menus that induce self-selection. Together, these frameworks explain why markets for insurance, credit, labor, and used goods systematically deviate from the competitive ideal and why institutions like warranties, credentials, and regulation exist.

When to Use

• Diagnosing why a market is failing or shrinking (quality collapse, credit rationing, insurance death spirals)
• Evaluating whether a signal (degree, certification, warranty) is credible and efficient
• Designing screening mechanisms (menus, deductibles, trial periods) to sort heterogeneous agents
• Assessing policy interventions (mandatory disclosure, minimum standards, subsidized insurance)

When NOT to Use

• Information is symmetric or costlessly verifiable (no asymmetry problem)
• The product is a pure experience good where reputation and repeat purchase fully resolve quality uncertainty
• The analysis requires modeling strategic interaction beyond bilateral (use full game-theoretic models)

Assumptions

IRON LAW: Information asymmetry causes market failure — without
corrective mechanisms (signals, screens, warranties), bad drives out
good. Markets with severe adverse selection can unravel completely
(Akerlof's lemons result).

• One party (informed) has private information about quality, risk, or effort
• The other party (uninformed) cannot directly observe the relevant characteristic
• Agents are rational and respond to the information structure strategically
• Signals are costly, and the cost differs by type (single-crossing / Spence-Mirrlees condition)
• In competitive markets, cross-subsidization between types is unsustainable

Methodology

Step 1 — Identify the Information Asymmetry Classify: (a) Adverse selection (hidden type, pre-contractual) — the informed party's type affects the uninformed party's payoff; (b) Moral hazard (hidden action, post-contractual) — the informed party's effort is unobservable; (c) Both present simultaneously. Identify who is informed and who is uninformed.

Step 2 — Model the Market Failure