Measuring production yield for processes with multiple characteristics

Numerous capability indices have been proposed to measure the performance of processes with multiple characteristics. The index provides an exact measure on the production yield of multinormal processes in which the characteristics are mutually independent. In this paper, we thoroughly investigate the relationship between process parameters and the sampling distribution of . Our investigation shows that for a fixed , the variance of sample estimator of is restricted in an interval. For reliability consideration, the maximal variance is used in the estimation and testing of the production yield to ensure the level of confidence. Also, information about sample sizes required for specified precision of estimation and for convergence is determined. At last, we implement a trivariate process with data collected from a plastics manufacturing industrial to demonstrate the practicability of the proposed method in measuring the production yield.