Instrument abstention
The rule that a measurement instrument reports no number when its signal cannot be distinguished from its own noise; for posture dispersion, Z is reported only when between-posture spread clears the replicate noise floor at a declared significance level.
First used in Ariadne's Thread
A system that always emits a number misleads when noise rivals signal. The test compares the between-posture mean square with the within-posture mean square. Under the null of no posture effect the ratio follows an F distribution, and a permutation version gives a distribution-free guarantee. Abstaining unless the test rejects controls the long-run rate of falsely declaring a noise gate open.
The test is conservative in small designs: at five postures and three replicates, the power to detect a posture effect equal to the noise is only about one half, so sensitivity must be bought with replicates. Reporting only on rejection also inflates values near the threshold, which is why the rule and its level are published with every study.
Abstention is the measurement form of a broader Institute commitment: a refusal is preferable to an answer that cannot be defended.
Related terms
Related frameworks
Posture Dispersion (Z)
Hold verified law fixed, vary only the judicial posture across a declared panel, subtract the instrument's own replicate noise, and the normalized dispersion that remains, Z, measures how open a procedural question is.
The Four Laws of System Design for Computational Law
A legal AI system must never overstate its confidence, must explain every output, must ground every legal proposition in validated authority, and must keep its reasoning components testable and versioned, with each law yielding to the laws above it.