Process capability indices: overview and extensions

The process capability indices C-p, C-p*, CPL, CPU, CPL*, CPU* C-pk C-pk* C-pm and C-pm*, are presented and related to process parameters. These indices form a complementary system of measures of performance and are used by a number of U.S. and Japanese industries. Some properties of an estimator of C-pm, (C) over cap (pm) are given, and the operating characteristic curve approach is used to analyze ((C) over cap (p), (C) over cap (pm) and (C) over cap (pm)* where (C) over cap (p) and (C) over cap (pm)* are estimators of (C) over cap (p) and (C) over cap (pm)* respectively. Two tables for the analysis and use of (C) over cap (p) and Cp,, are included, and an example of application of <(C())over cap>(p), (C) over cap (pm) and (C) over cap (pk) is provided, where (C) over cap (pk) is an estimator of (C) over cap (pk). Finally, criticisms and benefits of the use of process capability indices are presented, (C) 2002 Elsevier Science Ltd. All rights reserved.