nonmanipulability

Nonmanipulability is a property of a mechanism, process, or device whereby participants cannot benefit from misreporting information or acting strategically. In this sense, a nonmanipulable system elicits truthful behavior under its natural assumptions. The term is closely related to strategy-proofness or truthfulness in mechanism design and social choice theory.

In voting and allocation rules, nonmanipulability means that no voter (or coalition) can improve the outcome by misrepresenting preferences or choices. The Gibbard-Satterthwaite theorem shows that, for deterministic voting rules with unrestricted preference orders, every non-dictatorial rule is manipulable. This motivates studying restricted domains (such as single-peaked or single-crossing preferences) and rules designed for truthfulness. The VCG mechanism is often cited as strategy-proof in settings with quasi-linear utilities, though it requires specific assumptions about the domain and may raise budgetary or practical concerns.

Nonmanipulability also appears in auctions, market design, and some measurement and evaluation frameworks where designers aim to deter manipulation by bidders, participants, or data submitters. In practice, achieving perfect nonmanipulability is difficult; robustness to collusion, partial information, and changing preferences is challenging. Consequently, designers balance incentives, simplicity, and resilience when pursuing nonmanipulability.

See also: strategy-proofness, manipulation, mechanism design, voting theory, auction theory.