Definition of Stability:« Back to Glossary Index
Stability represents variation due to elapsed time. It is the difference between an individual’s measurements taken of the same parts after an extended period of time using the same techniques.
Also, PROCESS STABILITY INDEX is often used in SPC where many charts are ranked by the %OOC (instability) due to application of control limits and alarm rules. Stability is not the same as Capability. Stability is based on statistical control limits, while Capability is based on customer specification limits. Often shown as %OOC and Cpk. But of course a Stable process has LOW %OOC near zero, but never zero long term if limits are set correctly due to false alarm rate with good limits and rules.
Stationary (lack of drift) is opposite of Dynamic. Not the same as Stability. Engineers and statisticians argue about these terms.« Back to Dictionary Index