Capability measures for processes with multiple characteristics

Process capability indices, such as Cp, Ca, and Cpk, have been widely used in the manufacturing industry providing numerical measures on process precision, process accuracy, and process performance. Capability measures for processes with a single characteristic have been investigated extensively. However, capability measures for processes with multiple characteristics are comparatively neglected. In this paper, we consider a generalization of the yield index Spk proposed by Boyles, for processes with multiple characteristics. We establish a relationship between the generalization and the process yield. We also develop a control chart based on the proposed general-ization, which displays all the characteristic measures in one single chart. Using the chart, the engineers can effectively monitor and control the performance of al