Abstract
Pearn and Chen (1997) proposed a class of capability indices Np (u, v) which generalize the process capability indices C p (u, v)(Vännman, 1995) to accommodate cases where the underlying distributions may not be normal. The current indices Np (u, v) are functions of quantiles which may not be known. In this article, we apply some existing quantile estimators to estimate the class of indices C Np (u, v). It is shown that the estimators of Np (u, v) we propose are all asymptotically normally distributed and equivalent and can perform better than the estimated C p (u, v) in some instances.