INCAPABILITY INDEX WITH ASYMMETRIC TOLERANCES

Greenwich and Jahr-Schaffrath (1995) introduced an index C-pp, a simpl e transformation of the index C(pm), which provides an uncontaminated separation between information concerning the process accuracy and pr ocess precision. Unfortunately, the index C-pp inconsistently measures process capability in many cases and thus reflects process potential and performance inaccurately. In this paper, we consider a generalizat ion, C ''(pp), to handle processes with asymmetric tolerances. The gen eralization is shown to be superior to the original index C-pp. In add ition, we investigate the statistical properties of a natural estimato r of C ''(pp) assuming the process is normally distributed.