ABSTRACT
This chapter describes proceed to define and examines the earliest form of process capability indices (PCI), generally denoted by Cp. The backlash against PCIs seems to come from two broad, and opposed, sources: a lack of appreciation of statistical theory and its applications; and a demand for precise statistical analysis, to exclusion of other constraints. J.T. Herman provides a thought-provoking criticism of the PCI concept, based on engineering considerations. Although it is useful to be aware of such relationships, it is much simpler to express them in terms of process mean and standard deviation, than in terms of PCIs. The Cpk index was introduced to give the value of ξ some influence on the value of the PCI. Relationships between Cp and Cpk are also discussed by A. Gensidy N.S. Barnett and D.E. Coleman. The numerator of Cpk is the distance of ξ from the nearer specification limit.
