Estimation of non-conformance using the modified tolerance region

This paper presents a method for estimating the proportion of non-conformance for correlated multivariate normal quality characteristics. The modified tolerance region is employed such that the method is robust in estimating probability of product quality failing to meet customer specifications. The results obtained from this method can be applied for measuring process performance and for predicting external failure costs. We demonstrate the proposed method using an example and compare the results based on both the modified tolerance region and the original tolerance region.