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Glossary · Reliability, calibration, and statistics

Multilevel splitting

Rare-event estimation by factorizing a very small failure probability into a product of larger conditional probabilities across severity levels, each estimated among the survivors of the previous level.

Defined in

Handbook · ValidationRare-event assuranceZero failures in n trials is not zero risk. Bound it, then prevent, search, oversample and monitor.
Importance sampling
Reweighting samples from a proposal distribution q to estimate expectations under the target p, by the likelihood ratio p(x)/q(x). For rare failures q over-produces failures; it must cover the failure region.
Robustness margin
A signed or graded distance to satisfying a formal or quantitative specification; useful for partial credit, early warning, and search.

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