Principal-Agent Problem vs Screening
Principal-Agent Problem and Screening are two Game Theory & Information concepts in AP Economics that students often mix up. The principal-agent problem arises when one party (the agent) acts on behalf of another (the principal) but has different incentives and better information. Screening is when a less-informed party designs choices to get an informed party to reveal hidden information. Here is how they compare side by side.
Examples include shareholders (principals) and CEOs (agents), or voters and politicians. Because the agent may pursue its own interests, principals use contracts, monitoring, and incentive pay to align goals.
Insurers offer different deductible–premium menus so high- and low-risk customers self-select; lenders use credit checks. Screening is the mirror image of signaling and helps reduce adverse selection.
Principal-Agent Problem vs Screening: A Situation Against a Technique
| Principal-Agent Problem | Screening | |
|---|---|---|
| What the term is | A problem you diagnose | A move the uninformed party makes |
| Who acts | The agent, out of the principal's sight | The uninformed party, by designing the options |
| What it concerns | Effort and care once the contract is running | Which type signs the contract at all |
| Information problem behind it | Usually a hidden action | A hidden type |
| Test of success | The agent chooses high effort in their own interest | Each type picks the option built for it |
| How the two meet | A principal may screen first and still face an effort problem after | A menu that sorts types says nothing about later effort |
A screening menu that is not incentive compatible sorts nobody
Screening works only when each type strictly prefers the option meant for it, and that condition fails more easily than students expect. Take an employer hiring from a pool where a high-ability worker produces 100 of output and a low-ability worker produces 60, and nothing at interview separates them. The menu offers a flat salary of 55 or a piece rate paying 80 percent of what the worker produces. Under the piece rate a high-ability worker earns 80 and a low-ability worker earns 48. The high-ability worker compares 80 with 55 and takes the piece rate. The low-ability worker compares 48 with 55 and takes the salary. The two types have sorted themselves, and the employer clears 20 on one and 5 on the other without ever measuring ability directly. Now raise the salary to 85 to look generous. The high-ability worker compares 85 with 80 and takes the salary, the low-ability worker takes it too, and the menu collapses into one pooled contract that reveals nothing and loses 25 on every low-ability hire. The comfortable-looking option has to be made deliberately unattractive to the type it is not for.
Sorting the type leaves the effort question completely open
Suppose the menu worked and the employer now knows which contract each worker took. Nothing in that result tells the employer how hard anyone will work next month, and the agency problem is sitting there untouched. The distinction matters because the two failures look different from the outside. A screening failure looks like the wrong people coming through the door: an insurance pool packed with high-risk drivers, a lender's book full of borrowers who knew they would struggle. An agency failure looks like the right people behaving badly once inside: a salaried worker easing off, a fund manager taking risks the client would refuse. A single instrument can happen to address both, since the piece rate above sorts the types and also rewards effort afterward, but that is a convenience rather than a rule. When a prompt says the firm cannot tell good applicants from bad, answer with screening. When it says the firm cannot tell whether the worker is trying, answer with monitoring and incentives, and name the agency problem.
Frequently asked questions
Is screening a solution to the principal-agent problem?
Screening solves one part of the principal-agent problem, the part that happens before the contract starts. Sorting applicants by having them choose from a menu tells the principal which type it has hired, which is real progress against a hidden characteristic. What screening cannot do is control what the agent does afterward, and that needs incentives, monitoring or shared risk. Most real contracts carry both kinds of feature, and a well-written question will make clear which role it is testing.
Who moves first in screening?
The uninformed party moves first in screening, and that ordering is what separates it from signaling. An insurer publishes a menu of policies, or an employer posts two pay structures, and the informed party then reveals itself by choosing one. Signaling reverses the sequence: the informed party acts first by sending a costly message such as a guarantee or a qualification, and the uninformed party responds. Same information gap, opposite order of play.
Why do screening contracts look like bad deals?
Screening contracts carry unattractive features because the unattractiveness is what does the sorting. A policy with a large deductible, a job with low base pay, or a plan with a long waiting period is built so the type it is not aimed at turns it down. Strip out the harsh feature and both types accept, the menu pools into a single contract, and the uninformed side is back where it started with no way to price by type.
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