Statistica Sinica 8(1998), 253-262

INCAPABILITY INDEX WITH ASYMMETRIC TOLERANCES

K. S. Chen

National Chin-Yi Institute of Technology

Abstract: Greenwich and Jahr-Schaffrath (1995) introduced an index Cpp, a simple transformation of the index, which provides an uncontaminated separation between information concerning the process accuracy and process precision. Unfortunately, the index Cpp inconsistently measures process capability in many cases and thus reflects process potential and performance inaccurately. In this paper, we consider a generalization, ,to handle pr ocesses with asymmetric tolerances. The generalization is shown to be superior to the original index Cpp. In addition, we investigate the statistical properties of a natural estimator of assuming the proces s is normally distributed.

Key words and phrases: Asymmetric tolerances, estimation, incapability index.