- Short-term dispersion : variability within samples, excluding deviations. What the process is capable of at that moment.
- Overall dispersion : all observed variability, including drift.
- Cp, Cpk : short-term capabilities — potential. Cpk takes alignment into account.
- Pp, Ppk : Performance calculated based on overall variance — actual results.
- Compliance with the Law : the quality of the fit between the data and the chosen model. This determines the validity of all subsequent conclusions.
- Henry's Right : A graph in which a population following the fitted law aligns with a straight line.
- EWMA : exponentially weighted moving average, sensitive to small, sustained deviations.
- Overdispersion : variability greater than that predicted by the binomial or Poisson distribution, typical of large batches. This explains the Laney charts.
- Phase I : reference period used to establish control limits.
Appendix: Definitions
Reading time