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.