PROCESS CAPABILITY WITH ASYMMETRIC TOLERANCES

Many widely-used statistical packages and recent authors addressing process capability apply C(pm) in cases where tolerances are asymmetric. This can misrepresent process capability, and points to the need to apply appropriate capability measures in the asymmetric case. We compare and contrast six relatively unfamiliar capability indices appropriate for asymmetric tolerances to give them greater visibility and to help potential users choose among them. For some of these indices methods of estimation from process data have not been published; work on this is deferred to subsequent papers.