Stability Study (MSA Type 6)
Checks whether a measurement system stays constant over weeks or months — a reference part measured repeatedly on a control chart, complemented by a drift test.
Also known as: stability analysis, MSA Type 6, long-term stability
The stability study (MSA Type 6) is the time-based complement to the cross-sectional MSA types (bias, linearity, Gage R&R): a single reference part is measured repeatedly with the same measurement system over an extended period. The measurement series is plotted as an I-MR or x̄-R control chart and checked in two ways — point-wise special causes via the Nelson rules and a systematic, creeping trend via a linear drift test.
- Control limits are either estimated from a baseline subgroup of the study itself (`from-study`) or supplied externally (`given`, e.g. from a prior calibration)
- Verdict — `stable` (nothing notable), `marginal` (isolated hints), `unstable` (≥ 3 Nelson violations or a strong trend)
- One reference part per study — multiple reference parts are represented as multiple Type 6 instances side by side, not mixed into one study
See also
Used in
In the Algorithm Lab
Sources
- AIAG — Measurement Systems Analysis Reference Manual, 4th Edition (MSA-4)
- Robert Bosch GmbH — Qualitätsmanagement in der Bosch-Gruppe, Heft 10: Fähigkeitsuntersuchung von Messsystemen
- Nelson, L. S. — Technical Aids: The Shewhart Control Chart — Tests for Special Causes, Journal of Quality Technology, 16(4), 1984